Photoassimilatory and Photorespiratory Behaviour of Certain Drought Tolerant and Susceptible Tea Clones

Net photosynthetic rate (P _N) in the mother leaves was higher in the drought tolerant (DT) clones of tea (Camellia sinensis) while liberation of the fixed ¹⁴C in light from the mother leaves was higher in the drought susceptible (DS) clones. The DT clones translocated more photosynthates to the crop shoots (three leaves and a bud) from the mother leaf than the DS clones. Concentrations of RuBP carboxylase (RuBPC) or oxygenase (RuBPO) had no relationship with the drought tolerant nature of tea clones but their ratio correlated with the same. DT tea clones had higher catalase activity that could scavenge the hydrogen peroxide formed in the photorespiratory pathway and thereby reduced photorespiration rate (P _R). The ratio of RuBPC/RuBPO had a positive correlation with P _N and catalase activity. Negative correlation between RuBPC/RuBPO and P _R and between catalase activity and RuBPO activity was established.     

Agrobacterium tumefaciens-mediated transformation of embryogenic tissues of tea (Camellia sinensis (L.) O. Kuntze)

Embryogenic tissues of tea were cocultivated withAgrobacterium tumefaciens LBA4404. The plasmid pBi121, which contains the neomycin phosphotransferase II (nptII) gene providing kanamycin resistance as a selectable marker and the β-glucuronidase (uidA) reporter gene, was used as binary vector. The highest transformation frequency (12 transformants/g fresh weight [FW] of treated embryogenic tissue) was obtained with 5-day-old tissues grown in liquid medium and cocultivated withAgrobacterium for 2 d in the same medium but containing 50 μM acetosyringone. There was improvement in the recovery of kanamycin-resistant tissues when tissues were first grown for 10 d on a medium containing 350 mg/L Timentin to prevent bacterial overgrowth, before application of the selection pressure. Resistant tissues obtained after 6 wk on kanamycin-selection medium showed stableuidA expression. Polymerase chain reaction demonstrated the presence of the transgenes, while Southern hybridization confirmed their integration into the genome. Transgenic plants were regenerated from transformed tissues within 4 mo after coculture.     

Sequence of physiological responses in groundnut (Arachis hypogaea L.) subjected to soil moisture deficit

Responses of drought-tolerant (DT) and drought-susceptible (DS) pot-grown groundnut (Arachis hypogaea L.) varieties to changes in leaf relative water content (RWC) were studied. Water stress (WS) was imposed on 30-day-old plants for 2 weeks. Leaf RWC decreased significantly under WS conditions with simultaneous decrease in net photosynthetic rate (P _N) and stomatal conductance (g _s). Even though no significant difference was observed between DT and DS varieties with regard to RWC, DT varieties were able to maintain significantly higher P _N than DS varieties. Higher values of water use efficiency (WUE) were also observed in DT varieties during WS conditions. The decline in P _N due to WS could be attributed to both reduction in g _s (i.e. stomatal limitation) and to reduction in chlorophyll content (Chl). No significant difference in leaf area index (LAI) was found between DT and DS types and LAI was not reduced by WS. Significant differences were found among the studied groundnut varieties, but not between DT and DS types, in terms of root, aboveground, and total dry mass. These growth parameters significantly decreased under WS conditions. Based on the results, a sequence of physiological responses in groundnut crop subjected to WS was postulated.