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Plant grafting: new mechanisms, evolutionary implications.

Goldschmidt EE - Front Plant Sci (2014)

Bottom Line: Taxonomic proximity is a general prerequisite for successful graft-take and long-term survival of the grafted, composite plant.Grafting also has significant pathogenic projections.This has led to the formation of alloploid cells that, under laboratory conditions, gave rise to a novel, alloploid Nicotiana species, indicating that natural grafts may play a role in plant speciation, under certain circumstances.

View Article: PubMed Central - PubMed

Affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem Rehovot, Israel.

ABSTRACT
Grafting, an old plant propagation practice, is still widely used with fruit trees and in recent decades also with vegetables. Taxonomic proximity is a general prerequisite for successful graft-take and long-term survival of the grafted, composite plant. However, the mechanisms underlying interspecific graft incompatibility are as yet insufficiently understood. Hormonal signals, auxin in particular, are believed to play an important role in the wound healing and vascular regeneration within the graft union zone. Incomplete and convoluted vascular connections impede the vital upward and downward whole plant transfer routes. Long-distance protein, mRNA and small RNA graft-transmissible signals currently emerge as novel mechanisms which regulate nutritional and developmental root/top relations and may play a pivotal role in grafting physiology. Grafting also has significant pathogenic projections. On one hand, stock to scion mechanical contact enables the spread of diseases, even without a complete graft union. But, on the other hand, grafting onto resistant rootstocks serves as a principal tool in the management of fruit tree plagues and vegetable soil-borne diseases. The 'graft hybrid' historic controversy has not yet been resolved. Recent evidence suggests that epigenetic modification of DNA-methylation patterns may account for certain graft-transformation phenomena. Root grafting is a wide spread natural phenomenon; both intraspecific and interspecific root grafts have been recorded. Root grafts have an evolutionary role in the survival of storm-hit forest stands as well as in the spread of devastating diseases. A more fundamental evolutionary role is hinted by recent findings that demonstrate plastid and nuclear genome transfer between distinct Nicotiana species in the graft union zone, within a tissue culture system. This has led to the formation of alloploid cells that, under laboratory conditions, gave rise to a novel, alloploid Nicotiana species, indicating that natural grafts may play a role in plant speciation, under certain circumstances.

No MeSH data available.


Related in: MedlinePlus

A range of citrus graft union shapes, presumably indicating rootstock-scion compatibility (reproduced from Webber, 1948; with permission).
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Figure 1: A range of citrus graft union shapes, presumably indicating rootstock-scion compatibility (reproduced from Webber, 1948; with permission).

Mentions: As already pointed out by Moore (1984), as yet there is no evidence for a specific biochemical-immunological recognition/rejection mechanism between the graft components. This is in contrast to pollination incompatibility, where specific mechanisms have been identified (Kao and Huang, 1994; Takayama and Isogai, 2005; De Franceschi et al., 2012). Yet, heterograft incompatibility clearly increases with genetic distance (Schöning and Kollmann, 1997; Flaishman et al., 2008), indicating some kind of physiological rejection. On the other hand, incompatibility occurs even among related genera of the same family in a rather unpredictable fashion. Thus, within the Solanaceae, reciprocal grafts of tomato (Solanum lycopersicum L.) and pepper were considered severely incompatible, whereas tomato and eggplant (Solanum melongena L.) only moderately so, in comparison with compatible tomato homografts (Kawaguchi et al., 2008). Considerable variation in degree of compatibility was evident among grafts of melon (Cucumis melo L.) onto 22 Cucurbitae rootstocks (Edelstein et al., 2004) and among other Cucurbitae species (Lee and Oda, 2003) and among chestnut (Castanea) species (Huang et al., 1994). In citrus trees, visual inspection of trunks at the graft union was believed to reflect the degree of compatibility (Figure 1, reproduced from Webber, 1948), although some graft combinations proved to be successful despite the unsmooth graft union (Wutscher, 1979). Anatomical follow-ups of heterograft unions invariably disclose mild to severe interferences with the formation of a fully functional stock/scion continuum. Changes in vascular anatomy were evident in grafts of apple (Malus domestica Borkh. and sweet cherry (Prunus avium L.) onto dwarfing rootstocks (Soumelidou et al., 1994; Olmstead et al., 2006) and even in compatible graft unions among Pinus species (Darikova et al., 2013). A commonly observed disturbance is a convolution of the vascular elements orientation (Soumelidou et al., 1994; Flaishman et al., 2008; Kawaguchi et al., 2008). Soumelidou et al. (1994) proposed that wound-induced changes in the normal flow of endogenous auxin, which plays a key role in vascular differentiation (Aloni, 1995; Cano-Delgado et al., 2010), might be responsible for this distortion. This hypothesis is supported by the recent study of Yin et al. (2012) who demonstrated the involvement of auxin in early stages of graft union formation. The oxidative stress symptoms reported by Aloni et al. (2008) appear only at a considerably later stage and may represent a belated response to the auxin imbalance.


Plant grafting: new mechanisms, evolutionary implications.

Goldschmidt EE - Front Plant Sci (2014)

A range of citrus graft union shapes, presumably indicating rootstock-scion compatibility (reproduced from Webber, 1948; with permission).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4269114&req=5

Figure 1: A range of citrus graft union shapes, presumably indicating rootstock-scion compatibility (reproduced from Webber, 1948; with permission).
Mentions: As already pointed out by Moore (1984), as yet there is no evidence for a specific biochemical-immunological recognition/rejection mechanism between the graft components. This is in contrast to pollination incompatibility, where specific mechanisms have been identified (Kao and Huang, 1994; Takayama and Isogai, 2005; De Franceschi et al., 2012). Yet, heterograft incompatibility clearly increases with genetic distance (Schöning and Kollmann, 1997; Flaishman et al., 2008), indicating some kind of physiological rejection. On the other hand, incompatibility occurs even among related genera of the same family in a rather unpredictable fashion. Thus, within the Solanaceae, reciprocal grafts of tomato (Solanum lycopersicum L.) and pepper were considered severely incompatible, whereas tomato and eggplant (Solanum melongena L.) only moderately so, in comparison with compatible tomato homografts (Kawaguchi et al., 2008). Considerable variation in degree of compatibility was evident among grafts of melon (Cucumis melo L.) onto 22 Cucurbitae rootstocks (Edelstein et al., 2004) and among other Cucurbitae species (Lee and Oda, 2003) and among chestnut (Castanea) species (Huang et al., 1994). In citrus trees, visual inspection of trunks at the graft union was believed to reflect the degree of compatibility (Figure 1, reproduced from Webber, 1948), although some graft combinations proved to be successful despite the unsmooth graft union (Wutscher, 1979). Anatomical follow-ups of heterograft unions invariably disclose mild to severe interferences with the formation of a fully functional stock/scion continuum. Changes in vascular anatomy were evident in grafts of apple (Malus domestica Borkh. and sweet cherry (Prunus avium L.) onto dwarfing rootstocks (Soumelidou et al., 1994; Olmstead et al., 2006) and even in compatible graft unions among Pinus species (Darikova et al., 2013). A commonly observed disturbance is a convolution of the vascular elements orientation (Soumelidou et al., 1994; Flaishman et al., 2008; Kawaguchi et al., 2008). Soumelidou et al. (1994) proposed that wound-induced changes in the normal flow of endogenous auxin, which plays a key role in vascular differentiation (Aloni, 1995; Cano-Delgado et al., 2010), might be responsible for this distortion. This hypothesis is supported by the recent study of Yin et al. (2012) who demonstrated the involvement of auxin in early stages of graft union formation. The oxidative stress symptoms reported by Aloni et al. (2008) appear only at a considerably later stage and may represent a belated response to the auxin imbalance.

Bottom Line: Taxonomic proximity is a general prerequisite for successful graft-take and long-term survival of the grafted, composite plant.Grafting also has significant pathogenic projections.This has led to the formation of alloploid cells that, under laboratory conditions, gave rise to a novel, alloploid Nicotiana species, indicating that natural grafts may play a role in plant speciation, under certain circumstances.

View Article: PubMed Central - PubMed

Affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem Rehovot, Israel.

ABSTRACT
Grafting, an old plant propagation practice, is still widely used with fruit trees and in recent decades also with vegetables. Taxonomic proximity is a general prerequisite for successful graft-take and long-term survival of the grafted, composite plant. However, the mechanisms underlying interspecific graft incompatibility are as yet insufficiently understood. Hormonal signals, auxin in particular, are believed to play an important role in the wound healing and vascular regeneration within the graft union zone. Incomplete and convoluted vascular connections impede the vital upward and downward whole plant transfer routes. Long-distance protein, mRNA and small RNA graft-transmissible signals currently emerge as novel mechanisms which regulate nutritional and developmental root/top relations and may play a pivotal role in grafting physiology. Grafting also has significant pathogenic projections. On one hand, stock to scion mechanical contact enables the spread of diseases, even without a complete graft union. But, on the other hand, grafting onto resistant rootstocks serves as a principal tool in the management of fruit tree plagues and vegetable soil-borne diseases. The 'graft hybrid' historic controversy has not yet been resolved. Recent evidence suggests that epigenetic modification of DNA-methylation patterns may account for certain graft-transformation phenomena. Root grafting is a wide spread natural phenomenon; both intraspecific and interspecific root grafts have been recorded. Root grafts have an evolutionary role in the survival of storm-hit forest stands as well as in the spread of devastating diseases. A more fundamental evolutionary role is hinted by recent findings that demonstrate plastid and nuclear genome transfer between distinct Nicotiana species in the graft union zone, within a tissue culture system. This has led to the formation of alloploid cells that, under laboratory conditions, gave rise to a novel, alloploid Nicotiana species, indicating that natural grafts may play a role in plant speciation, under certain circumstances.

No MeSH data available.


Related in: MedlinePlus