Hill Reaction, Photosynthesis and Chlorophyll Content in Non-Sugar-Producing (Turnip, Brassica rapa L.) and Sugar-Producing (Sugar beet, Beta vulgaris L.) Root Crop Plants

A pot experiment was conducted at the Botany Department, A.M.U., Aligarh, on 2 root crop plants, viz. turnip (Brassicarapa L.), non-sugar-producing and sugar beet (Beta vulgaris L.), sugar-producing, to compare their physiological activity (Hill activity,photosynthesis and chlorophyll content). The seeds of each plant were sown in 20 pots (80% soil + 20% FYM) separately. Two samplings were done at 125 and 140 days (after sowing). Hill activity was measured spectrophotometrically using DCPIP indicatorand photosynthesis was assayed by LICOR-6200 Photosynthesis System. Sugar beet gave the maximum leaf-area, Chl a/b ratio,stomatal conductance and photosynthesis rate and Hill activity at 125 days. However, the total chlorophyll was higher in turnip atboth stages than sugar beet. The stomatal resistance was maximum in turnip at 140 days and minimum in sugar beet at 125 days.The data show that chlorophyll contents are not related to the photosynthesis rate. The latter was most profound in sugar beet atboth stages as considerable amounts of photosynthates are transformed into sucrose and therefore sugar beet contains over 20% sugar by weight.