Characterization of photosynthetic events and associated changes in various clones of tea(camellia sinensis l) under low temperature conditions

Low temperature is one of the major environmental factors determining the growth rate ofCamellia sinensis (L.), and photosynthesis is one major metabolic process commonly used as a tool for identifying low temperature stress effects on plants. The Fv/Fm values at 6:30 a.m. (300-400 umol m-2s-1) did not vary much between the clones of tea plants. Further, when the light incidence increased at mid noon hours (1700-1800 µmol m-2s-1), the Fv/Fm values recorded a decline, irrespective of the clones. Of the 10 clones of tea plants under investigation, 3 clones, namely CRA-6017, TTL-6 and SMP-1, recorded a sharp decrease in the Fv/Fm ratio by 2 p.m. The malondialdehyde (MDA) levels in all the clones increased from 9 a.m. (1500-1700 µmol m-2s-1) to 2 p.m. and from 4:30 p.m. (900-1100 µmol m-2s-1) onwards it started to decrease and reach the levels equivalent to 6:30 a.m. by 7 p.m. (5–10 µmol m-2s-1 ). But the clones of TTL-1, TTL-4 and UPASI-9 showed low temperature tolerance as appeared in chlorophyll a fluorescence response. They showed a higher percentage increase in MDA levels, as compared to TTL-6, CRA-6017 and SMP-1, which showed low temperature susceptibility. But the reduction in the level of MDA by 4:30 p.m. (recovery) was faster in the clones TTL-1, TTL-4 and UPASI-9, as compared to TTL-6, SM/OM/54 and SMP-1. The result indicates that in TTL-6, SMP-1 and SM/ OM/54, the toxic oxygen species scavenging mechanisms may be less functional as compared to other clones. The percentage increase of proline and carotenoids was higher in clones TTL-1, TTL-4 and UPASI-9 as compared to TTL-6, CRA-6017 and SMP-1.