Dissertation Abstract

Short Photoperiod Induction of Endodormancy: Comparative Studies of Three Vitis Genotypes

Short photoperiod induction of endodormancy has been observed in many woody species. In Vitis (grapes), depth of endodormancy induction is indicated by the presence or absence of budbreak after pruning. Three genotypes (V. riparia, V. spp. 'Seyval Blanc' and their F$\sb1$ (V. riparia x 'Seyval Blanc')) were monitored for morphological and physiological endodormancy responses during six weeks of short (8 h, SD) and long (15 h, LD) climate-controlled photoperiod treatments. After four weeks of SD, V. riparia were endodormant, as indicated by several morphologic changes. Longitudinal growth had ceased and terminal meristems had yellowed and abscised. A dramatic decrease in bud water content was observed and buds failed to break and grow after pruning.

'Seyval Blanc' maintained actively growing meristems with no abscission throughout treatment, and little or no delay in budbreak. Only moderate decreases in bud water content were observed after six weeks of SD treatment.

The F$\sb1$ plants displayed an intermediate response to SD treatment. Growth cessation, tip abscission and bud endodormancy occurred in this genotype after six weeks of SD treatment.

Periderm development and coloration occurs naturally with age-related maturation. Although periderm development is more extensive after SD, it is not an adequate determinant of endodormancy intensity.

10% discontinuous SDS-PAGE protein profiles demonstrated SD-induced changes in polypeptide accumulation. Two, three and five-fold increases in relative abundance of a 19 kDa polypeptide were observed after six weeks of SD treatment in 'Seyval Blanc', the F$\sb1$ genotype and V. riparia, respectively.

Polypeptides from buds of all three genotypes, with pIs between 7.6 and 4.7, were resolved by two-dimensional gel electrophoresis. The 2-D gel analyses confirmed SD-induced and maturation related changes in polypeptide accumulations observed in the 1-D study.

Free-solution IEF was used to examine a larger polypeptide pI range and recover more protein for further analysis. Results indicate (1) the presence of a 23 kDa, heat-stable polypeptide (pI 7.0) that increases with maturation in all three genotypes, with the highest accumulation in V. riparia. (2) The 17 kDa band observed in the 1-D study represents at least three polypeptides of differing isoelectric points. One of these (17 kDa, pI 7.0) is heat stable and appears in V. riparia after four weeks of SD. (3) The 19 kDa band also appears to contain several polypeptides of differing pI's.

The total amino acid compositions of V. riparia's 19 and 17 kDa and 'Seyval Blanc's 19 kDa polypeptides were analyzed. The Kyte and Doolittle hydropathy index (1982) was used to determine compositional bias.

The first 12 N-terminal amino acid residues were determined for the V. riparia 19 kDa (pI 6.9) and 17 kDa (pI 7.0) polypeptides. Protein databank analysis showed sequence homology for both of them to abscisic acid-responsive (66%), pathogenesis-related (63-80%) and allergen (63-81%) proteins in other herbaceous and woody species. (Abstract shortened by UMI.)

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