Now, who can tell me, it it the scion or the mother tree that generates the callous? Or both? It seems to me the scion is very important to the process.
I’m going to argue that it’s the mother tree, i.e., the growing part. I don’t see how the scion would have the energy to do it. I imagine (key word there) that it’s the same thing as callous growing over the area left when a branch is cut back.
Of course the scion has stored energy and then when it leafs out it begins generating new energy and, from my experience, carbo’s seem to be transported “downhill” or towards the trunk. It seems logical to me that the scion is where the healing comes from but I was hoping someone had some researched info.
Not that I mind your guessing and I’m not saying my guess is better than yours, but not because I don’t think it is but because it would be obnoxious to say so. 
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Well, could it be that one initiates it and the other then joins in? And if so, which is which?
Just guessin’ …
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I’m callusing grape cuttings now in preparation for rooting. That callus obviously forms from the cutting. I’d think the rootstock in a graft would also form callus. Both are trying to close a wound.
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my understanding is that carbs/proteins/minerals are supplied from below(mostly from roots) when trees start leafing out in spring, and then at some point-- when the leaves have fully differentiated during growing season, the carbs and protein flow will be reversed. Then next spring, the net flow will be reversed anew
both will generate the callus. Even hard-to-root species will callus “downward” on their own as cuttings, relying on the scant supplies of energy/proteins/ minerals/moisture within the stems. The rootstock is definitely more than able(compared to the scion) to callus in spring considering its ample food storage/moisture within the main trunk, and especially supplied by the roots from previous year’s photosynthesis.
actually just posted proof of “upward” callusing of an internodal segment of a stem(where nodes shouldn’t be present), wherein the stump’s callus didn’t just produce xylem and phloem, but also upped the ante by differentiating into nodes that leafed out.
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The carbs are manufactured by the leaves and the minerals extracted by the roots. I believe they move in opposite directions.
I think what Fruitnut said makes sense… my experience suggests that at the very least, the scion plays a major part in closing a wound and the sooner it leafs out after the graft the better things seem to work out. I use to think more time in scion dormancy would reduce the chance of dehydration before closure of the wounds, but no longer, especially with apple and pear grafts. Some of my best growing grafts are the result of using scionwood harvested after first growth and promptly grafted to trees without storage in refrigeration (which makes scion buds slower to come out of dormancy). The first growth of scionwood I use is on the discarded tips, and not the buds on the scionwood itself.
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yes, minerals can only be extracted by the roots(in absence of foliar fertilization)…
and while carbs/proteins can only be manufactured by foliage, most of it will be stored in roots which will be used by the tree coming out of dormancy next spring. There will be a net upward flow of carbs and proteins from the roots when tree comes out of dormancy in spring compared to downward flow, since leafing out entails use of resources, and only when the leaves have been fully developed will the net flow be reversed.
Where do you get that info. Roots store carbs, I know, but so do buds and so does wood. If the roots were so generous with their stored energy, why do commercial growers spray spur buds with foliar urea in spring and why does the literature talk about fall N fertilization being a means to get N into buds during the fall so it is available in early spring by already being located in the buds? In all the years I’ve been reading about plants and in all the books I’ve ever read about arboriculture I’ve missed your claim.
If you are correct, I’ve somehow missed it in my 60 year relationship with fruit trees and would be excited to learn somethin so new to me. But my first reaction is strong skepticism, I have to admit.
Hi @alan, weight-for-weight, roots generally have the highest concentrations of utilizable carbs, especially starches(which–apart from wood, is the densest of all carbohydrates calorically speaking). The only difference between wood and starch is that wood cannot be used as energy source by the plant, whereas starch is ready to be hydrolyzed into soluble/simple sugars. Sweet potatoes and other root crops are the most extreme examples of starch storage. Of course stems and leaves have sugars and starch too as shown on the graph below.
i have heard of that too, as reportedly deciduous species’ roots don’t absorb nitrogen from the soil in early spring and is limited to nitrogen/nitrogenous compounds absorbed from the soil the previous summer or fall, so i guess the idea is to spray above-ground when below-ground is not working. Btw, nitrogen/urea is more of a mineral, and not a source of energy, so couldn’t really figure out your query
The answer to your question requires further research per this article that references [[Hartmann and Kester, (2002)]
My hunch from reading Hartmann & Kester is that the cells that divide to form the callous bridge must come from both which is how compatibility is determined. A scion is as much alive as the rootstock so it makes sense that the energy stored in the scion in form of pectins would be just as available as those in the rootstock, assuming they are compatible!
Dennis, Kent, wa
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btw @Alan, i looked up nitrogen-and-starch relations in deciduous species, and found below.
It also answered your question regarding starch concentration difference between roots and stem, and also gave me some info about how nitrogen can influence production of carbs.
Also mentions of amount of starch in both roots and stems being highest during pre-dormancy(which is expected since they were loaded by photosynthesis from spring to fall), and lowest during leafing out in spring, which is to be expected since stems and roots are the providers of sugars to fuel bud growth in the absence of full- differentiated leaves.
Abstract
Seasonal changes in starch were studied at the tissue and cellular levels in roots and stems of Salix viminalis L. cuttings. Cuttings were planted in pots containing sand and grown in a controlled environment chamber in which seasons were artificially induced by changes in temperature and photoperiod. Nitrogen was supplied at optimum and low rates, and during dormancy, one-half of the plants were decapitated. Starch concentrations in root and stem tissues were determined regularly during shoot extension growth, dormancy and resprouting after dormancy. We used light microscopy (LM) combined with image analysis (IA) to determine the cellular localization and amount of starch in different cell types of stem and root tissues. Chemical analysis confirmed that starch concentrations were lower in plants receiving a high-N supply rate than in plants receiving a low-N supply rate. In all plants, the highest concentration of starch was in the roots. Light microscopy and IA showed that starch accumulated mainly in the phloem and cortical cells of both root and stem tissues. Starch grains were also regularly found in ray parenchyma cells. The amount of starch as well as the size of the grains showed strong seasonal fluctuations. In both roots and stems, starch concentrations were highest during predormancy and lowest during periods of shoot extension growth. At the time of resprouting, root cells of decapitated plants were more depleted of starch than root cells of intact plants, supporting the hypothesis that starch reserves in roots are important during the early phase of resprouting in coppice systems.
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OK, that’s interesting, but there is not a word about the upward movement of the starch. The first growth in spring seems to be fine roots and fine roots are needed to deliver water and other nutrients to the growing shoots in spring- they are the most dynamic part of the root system that do most of the “work”. How much of the stored carbos in the roots are being used to form new roots? How much, if any, is being shuttled to the growing shoots?
I truly appreciate the links, but what you stated as fact doesn’t even appear to be a hypothesis in the articles you linked. To get the growth going the roots would require stored carbs whether it was for new root growth are to share with growing shoots.
One thing I will say from experience, it you transplant a tree damaging most of the FINE root system (which occurs even when you ball and burlap trees with typical tree diameter to ball size ratios, but also when you bare root them). and attempt to put new grafts on it, survival of grafts will likely be poor and scion growth the first season tepid (as well as all other shoot growth). When I transplant trees bareroot saving almost all of the large roots in the process, trees still experience varying levels of transplant shock, although that would presumably save almost all of the stored carbs.
It is amazing to me that something as important as the shuttling back of carbs from the roots to growing shoots is not clearly known quantitatively if it is an important source of energy for the growing shoots.
But I’m no scientist.
Nevertheless, an interesting discussion to me. Thank you.
the most tangible proof of that would be sweet potatoes i just mentioned. Sweet potatoes are roots, and many of them from grocery stores are still alive once get placed(and forgotten)on our kitchen counters. In a couple of weeks at room temps, they will start sprouting out de novo stems and leaves, even in total darkness(much like they would if you plant them deep in the ground). The yams shrink and get wrinkly as a result of the moisture/starches/sugars within getting consumed. Stems are mostly cellulose fibers, and cellulose fibers are carbs. Those wouldn’t have formed if not for the carbs within the roots, since the yams are in darkness and have yet to unfurl their solar panels(foliage)
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forgot to mention something even more tangible an analogy since many of us are orchardists and not sweet potato farmers–am sure many of us dug up apple or plum trees and transplanted them somewhere.
we often leave remnants of their roots where those trees used to be plnted. And those will try to regenerate de novo stems using their internal food supplies . Being in total darkness-- they are in crisis do-or-die mode
of course-- most plants will use carbs/starch reserves first from their stems/trunks(due to proximity to the buds)before using their root reserves, but carbs stored in roots will rise to the occasion(literally and figuratively 
) in case of plants suddenly getting deprived of light, or if the roots get severed from mother tree and have to regenerate
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They way I’m hearing it, you have an opinion based on logical leaps and not on what is known. However your opinion is more informed than mine was when we began this discussion, so I’m grateful, but you probably should acknowledge that your opinion is purely speculative no matter how logical. Science begins with such speculation but I think it should be represented accurately or things can get very confusing. One doesn’t necessary end up on solid land when they make a logical leap. My own logical leaps, especially ones based on anecdote often end up being contradicted by an uncooperative
and contradicting reality. It is fun though, when they pan out.
This seems to explain the state of the science well and is it basis of this comment… maybe you can find something more recent with newer research.
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This contradicts my previous opinion and I concede my mistake. I thought that carbs only ran “downhill”… I didn’t assume it but I believed it nevertheless.
I appreciate being corrected.
I thought I should make that clear.
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i admit it is a logical viewpoint on my part. It is just that i couldn’t find any way jujube roots(which we regularly poach during winter) would be able to leaf out in spring without using their internal reserves. And admittedly adamantly preach to all would-be recipients(of those root cuttings) to plant them horizontally, and shallowly, with just enough soil cover to prevent desiccating the specimen. Planting them deep would be a huge drain on the root segments’ finite reserves as the shoots will have to develop long stems before they could access sunlight. The longer the would-be stem has to grow upwards (without access to sunlight) the more likely for the roots’ food storage to be depleted.
Anyway, below was a most critical excerpt from that reference you just posted , quite validating to see is congruent with my “speculative logic”
Radioisotope labeling studies
The best evidence for the role of roots in early season growth
comes from labeling studies. Kandiah (1979b), Quinlan (1969), and
Hansen and Grauslund (1973) all showed that, at budbreak, labeled
carbohydrates from apple roots were translocated to the first formed
leaves and also to flowers (Quinlan, 1969; Hansen and Grauslund,
1973). In pecan, Lockwood and Sparks (1978a, 1978b) found most
of the label from root reserves in the first formed leaves, but also
found the same reserves in leaves formed well after budbreak, as
well as in male and female inflorescences. Similar data have already
been mentioned for grape.
while the above has been proven, it may be species-dependent, and food-accumulation dependent. Trees which have maxed out photosynthesis the previous year will likely not need any carbs from the roots since already “fully loaded” at the buds and stems.
we also preach(speculatively, yet again) to jujube recipients in more northerly latitudes that the best way of conferring some tolerance to deep freezes would be to plant their jujubes at spots on their yards which get the most hours of sunlight to max out photosynthesis. May sound contradictory that for a specimen to be cold-hardy in winter-- the specimen should get as much direct heat in spring and summer… Anyway, this is because the more sugars are stored in the stems, the more likely to have anti-freeze effects which minimize stem splitting/die-back.
Yes, I notice several references of some carb movement from roots to buds, but it seems the amount of it is unknown. I’ve learned something from this discussion, but I hope I’m not the only one.
That was the statement I originally responded to, and though my response was mistaken yours seems, at the very least, overblown in light of what we’ve dug up in established research. I found no information about overall percentage of contribution from roots and the suggestions seem to be that the roots contribute but don’t dominate the carb source for emerging buds. The majority of stored energy may be in the roots but that doesn’t mean that the overall contribution to shoots dwarfs what’s already in buds and nearby wood, especially when we don’t know how much is required to generate new roots and respiration throughout fall, winter and early spring.
Do you agree with that… or am I missing something?