Ys. Chauhan et T. Senboku, THERMOSTABILITIES OF CELL-MEMBRANE AND PHOTOSYNTHESIS IN CABBAGE CULTIVARS DIFFERING IN HEAT TOLERANCE, Journal of plant physiology, 149(6), 1996, pp. 729-734
Responses of two Japanese cabbage (Brassica oleracea L. var capitata)
cultivars, heat tolerant Sousyu and heat-susceptible YR Kinshun, were
compared in terms of cell-membrane thermostability, chlorophyll fluore
scence, chlorophyll A and chlorophyll B contents, and photosynthetic r
ates. High (similar to 50 degrees C) temperature caused greater relati
ve injury and reduction in the values of fluorescence in YR Kinshun th
an in Sousyu, especially when non-hardened for 24h prior to the measur
ement. Hardening at 30-35 degrees C improved the thermostabilities of
cell-membrane and chlorophyll fluorescence and decreased the chlorophy
ll content, and consequently photosynthetic rates in YR Kinshun. Chlor
ophyll content and chlorophyll fluorescence of Sousyu were relatively
less adversely affected by the hardening and stress temperatures. Sous
yu maintained higher chlorophyll content and rates of photosynthesis t
han the YR Kinshun in hardened condition whereas differences between t
he two genotypes were small in non-hardened condition. Heating leaves
at 50 degrees C reduced photosynthetic rates of both the cultivars. So
usyu, however, maintained higher rates than YR Kinshun even after the
heat treatment. The results suggest that higher thermostability of cel
l membranes, chlorophyll fluorescence and photosynthetic rates of Sous
yu, especially under non-hardened condition, may give it an overall ad
vantage in high temperature environments over YR Kinshun.