Lily Kaveeta

Effects of brassinosteroid and brassinosteroid mimic on photosynthetic efficiency and rice yield under heat stress

Brassinosteroids (BRs) have been reported to counteract various stresses. We investigated effects of exogenously applied brassinosteroid, 24-epibrassinolide (EBR), and brassinosteroid-mimic compound, 7,8-dihydro-8α-20-hydroxyecdysone (DHECD), on the photosynthetic efficiency and yield of rice (Oryza sativa L. cv. Pathum Thani 1) under heat stress. Solutions (1 nM) of EBR and DHECD were separately sprayed onto foliage of individual rice plants during their reproductive stage. Five days after the application, the plants were transferred to the day/night temperature regime of 40/30°C for 7 days and then allowed to recover at normal temperature for 7 days. We demonstrated that both DHECD and EBR helped maintain the net photosynthetic rate. The DHECD and EBR application enhanced stomatal conductance, stomatal limitation, and water-use efficiency under the high-temperature regime. DHECD- and EBR-treated plants showed an increase in the nonphotochemical quenching that was lower than that in the control plants. Moreover, DHECD and EBR treatments maintained the maximal quantum efficiency of PSII photochemistry and the efficiency of excitation capture of the open PSII center. Furthermore, the treatments with DHECD or EBR resulted in higher chlorophyll content during the heat treatment compared with the control plants. The paddy field application of 1 nM EBR and/or 1 nM DHECD at the reproductive stage during the hot season could increase the rice yield, especially, the number of filled seeds. DHECD and EBR enhanced total soluble sugar and reducing sugar in straw and more starch was accumulated in rice seeds. Consequently, our results confirmed that DHECD showed biological activities mimicking EBR in the improvement of photosynthetic efficiency and in rising the rice yield under heat stress.

Variation in ion accumulation as a measure of salt tolerance in seedling and callus of Stylosanthes guianensis

Seedlings of Stylosanthes guianensis CIAT 184 (Stylo 184) were germinated under salt-stress conditions (0-170.9 mM NaCl), and germination and ion content (Cl-, Na+, Ca2+, Mg2+ and K+) were measured after seven days. The salt treatment had no effect on the germination percentage, but the seedling showed reduced growth and displayed variation in ion uptake, thus accumulating Na+ and Cl- in the roots. Callus produced from seedlings selected as salt sensitive (T1) or salt tolerant (T2, T3, T4 and T5) was examined for growth and ion content under the influence of NaCl (0-256.4 mM NaCl) after 15 days. The sensitive clone (T1) contained the lowest Na+ and Cl- content with the highest percentage of K+ contributing to osmolality, suggesting it possesses an ion regulation mechanism that is typical of glycophytes; i.e., osmotic potential was adjusted by accumulating K+. The other clones (T2, T3, T4 and T5) expressed different strategies (osmotic adjustment) to cope with salt stress. T5 showed the highest mean dry weight on salt medium and displayed more effective ion regulation by maintaining low Na+:K+ and Na+:Ca2+ ratios. T2 expressed high Na+ and Cl- with the highest percentage of Na+ contribution to osmolality and water content (succulence). T3 and T4 had lower growth rates but similar ion regulation in relation to T5. Results indicated that the ion content can be used to discriminate salt sensitive and salt tolerant clones of Stylo 184.

Physical Properties of Traditional Thai Hemp Fiber (Cannabis sativa L.)

ABSTRACT Hemp (Cannabis sativa L.) from a traditional Thai variety was used as a source of fiber in this research. The variety has been grown for a long time by the Hmong, a hill tribe, for the purpose of textiles. Hemp was grown in Chiang Mai, in the North of Thailand. Fiber fineness, fiber strength, fiber length, and lignin content of bast fibers from the top, middle, and bottom part of hemp stems aged 65 and 120 days were measured after chemical separation. The results showed that the finest fiber was from the top of the stem. The fiber fineness determined from the airflow method varied from 14.2 to 27.0 FBAI200, and according to the OFDA method it varied from 14.1 to 19.1 μm. The highest strength fiber was from the middle part of the stem; fiber strength (Stelometer – collective test) varied from 10.9 to 27.4 cN/tex. Fiber length varied from 22.0 to 28.4 mm. At the early stages of male pollination, male plants had a lower lignin content than female plants. The measurement method, age of plant, and part of stem analyzed affected fiber properties. This traditional Thai hemp showed fine fiber and can be improved to a commercial level for the textile industry.