Investigating the role of polygalacturonase in cotyledonal cracking of green beans (Phaseolus vulgaris L.)
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Date
2005
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Abstract
Transverse cotyledonal cracking (TVC) was characterised at physiological,
biochemical and molecular levels in three common bean (Phaseolus vulgaris L.)
cultivars: Imbali, Tongaat and Tokai. The incidence of TVC was determined
visually on ten-day old seedlings and was expressed as the number of cracks per
plant. The effect of Ca++ on TVC incidence was examined by enhancing the
calcium content of seed cotyledons using calcium salts in seed priming and
coating. EDAX was used to quantify the cotyledonal calcium content. Activities
of the pectinolytic enzymes polygalacturonase (PG) and pectin methylesterase
(PME) were assayed at dry seed, VC, R4 and R6 phenophases of the bean
plant, and zymogram electrophoresis was used to identify the two enzymes. The
results showed that cultivars Imbali, Tongaat, and Tokai were susceptible
resistant and intermediate, respectively, with respect to TVC incidence. Calcium
uptake was higher in Tongaat cultivar (P= 0.05) compared with Imbali and Tokai,
irrespective of calcium salt enhancement. Vigour was significantly reduced (P<
0.01) by both coating and priming. TVC significantly lowered yield (P= 0.05) in
the susceptible Imbali cultivar. Zymogram analysis identified lytic bands at
~45kDa (PG gel) and ~30kDa (PME gel). The activity profile of PME was similar
for all cultivars. However, PG activity of susceptible Imbali was high in dry seeds
and at the R4 and R6 stages of plant development, whereas the more resistant
cultivars displayed high activity at the VC stage only. It is concluded that high
PG activity at R4 stage is a more reliable determinant of green bean propensity
to cotyledonal cracking.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
Keywords
Beans., Beans--Physiology., Beans--Varieties., Green beans., Phaseolus vulgaris., Plants, Effect of calcium on., Crop yields., Seeds--Physiology., Theses--Crop Science.