Biotechnological advances in tea (Camellia sinensis [L.] O. Kuntze): a review.

KEY MESSAGE: This article presents a comprehensive review on the success and limitations of biotechnological approaches aimed at genetic improvement of tea with a purpose to explore possibilities to address challenging areas. Tea is a woody perennial tree with a life span of more than 100 years. Conventional breeding of tea is slow and limited primarily to selection which leads to narrowing down of its genetic base. Harnessing the benefits of wild relatives has been negligible due to low cross-compatibility, genetic drag and undesirable alleles for low yield. Additionally, being a recalcitrant species, in vitro propagation of tea is constrained too. Nevertheless, maneuvering with tissue/cell culture techniques, a considerable success has been achieved in the area of micropropagation, somatic embryogenesis as well as genetic transformation. Besides, use of molecular markers, "expressomics" (transcriptomics, proteomics, metabolomics), map-based cloning towards construction of physical maps, generation of expressed sequenced tags (ESTs) have facilitated the identification of QTLs and discovery of genes associated with abiotic or biotic stress tolerance and agronomic traits. Furthermore, the complete genome (or at least gene space) sequence of tea is expected to be accessible in the near future which will strengthen combinational approaches for improvement of tea. This review presents a comprehensive account of the success and limitations of the biotechnological tools and techniques hitherto applied to tea and its wild relatives. Expectedly, this will form a basis for making further advances aimed at genetic improvement of tea in particular and of economically important woody perennials in general.

Influence of drought stress on cellular ultrastructure and antioxidant system in tea cultivars with different drought sensitivities.

Drought is the major yield-limiting abiotic factor of tea cultivation. In the present study, influence of drought stress on cellular ultrastructure and antioxidants was studied drought-tolerant (TV-23) and -sensitive (S.3/A3) tea cultivars by imposing drought stress for 21 days. Drought stress led to considerable structural alterations in mitochondria, chloroplast and vacuole. Lesser membrane integrity and higher structural damage was observed in S.3/A3. Chlorophyll a, chl-b and carotenoids content in leaves decreased in each cultivar; however, the decrement was more brisk in S.3/A3. Proline, total soluble sugar, ascorbic acid and abscisic acid were elevated in TV-23 whereas hydrogen peroxide, superoxide anion, lipid peroxidation and electrolyte leakage increased rapidly in S.3/A3. Starch content decreased both in leaves and roots of each cultivar and was more pronounced in roots of TV-23. Under drought, enhanced activities of ascorbate peroxidase, catalase, peroxidase and superoxide dismutase were recorded in both roots and leaves of each cultivar, but the rate of enhancement was more in TV-23. This indicated that tolerant cultivar exhibited higher antioxidant capacity and a stronger protective mechanism such that their ultrastructural integrity was better maintained during exposure to drought stress.

Zinc stress induces physiological, ultra-structural and biochemical changes in mandarin orange (Citrus reticulata Blanco) seedlings.

Zinc (Zn) is an essential micronutrient for higher plants; yet, at higher concentrations it is toxic. In order to explore the effect of Zn stress on growth, biochemical, physiological and ultra-structural changes, 1 year old mandarin plants were grown under various Zn concentrations (1, 2, 3, 4, 5, 10 15 and 20 mM) for 14 weeks. The biomass of the plants increased with increasing Zn concentrations and finally declined under excess Zn concentration but the prime increase was observed at 4 and 5 mM Zn. Zn stress reduced the photosynthetic rate, stomatal conductance, and transpiration along with reduction of chlorophyll a, chlorophyll b, and carotenoids content in leaf. Superoxide anion, malondialdehyde, hydrogen peroxide and electrolyte leakage were elevated in Zn stressed plants. The activities of ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), superoxide dismutase (EC 1.15.1.1) and peroxidase (EC 1.11.1.7) enzymes were increased in both Zn-deficient and Zn-excess plants. Therefore it is suggested that antioxidant defense system did not sufficiently protect the plants under rigorous Zn stress which was also corroborated by the alteration in cell ultrastructure as revealed by transmission electron microscopy.