Kanapol Jutamanee

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.

EFFECT OF SWINE MANURE EXTRACT ON LEAF NITROGEN CONCENTRATION, CHLOROPHYLL CONTENT, TOTAL POTASSIUM IN PLANT PARTS AND STARCH CONTENT IN FRESH TUBER YIELD OF CASSAVA

The effects of swine manure extract (SME) as foliar fertilizer (FSME), soil fertilizer (SSME), and both soil and foliar fertilizer (FNSSME) on leaf nitrogen (N) concentration, chlorophyll content, total potassium (K) in plant parts and starch content in the fresh roots, compared to a conventional, chemical fertilizer (CF) were studied in cassava cultivar ‘Hauybong 60’. The results showed that plants on FNSSME had the highest chlorophyll contents and SPAD values at four months after planting (MAP). Cassava plants treated with SSME and FNSSME had highest starch content and was significantly higher than in plants treated with CF and a FSME. There was a strong, positive relationship between the leaf nitrogen concentration and chlorophyll content in cassava at 6 MAP. The results of the study indicated that an application of FNSSME to cassava plants could provide a higher chlorophyll content and higher tuber quality of the plants than those applied with chemical fertilizer.

Promotive Effect of Priming with 5-Aminolevulinic Acid on Seed Germination Capacity, Seedling Growth and Antioxidant Enzyme Activity in Rice Subjected to Accelerated Ageing Treatment

Abstract: Seed deterioration by ageing caused by natural and artificial treatments lowers germinability and viability. Seed priming is a technique used to relieve seed deterioration from ageing. We evaluated the effect of seed priming with 5-aminolevulinic acid (ALA) at various concentrations on the seed germination capacity, seedling growth, antioxidant enzyme activities, and lipid peroxidation in the rice seedling cultivar Pathum Thani 1 with or without exposure to artificial ageing treatment. Seeds were subjected to accelerated ageing treatment by exposure to high relative humidity and high temperature conditions for 84 hr (aged seeds). The shoot length was significantly reduced and the injury index and H2O2 formation were increased in the seedlings emerged from the aged seeds. Priming of the aged seeds with 0.5 μg mL–1 ALA significantly enhanced the seed germination capacity and seedling relative growth rate to values higher than those obtained by priming with water (hydropriming). However, there was no significant difference in superoxide dismutase, peroxidase and ascorbate peroxidase activity as compared with hydropriming. In the seeds not given ageing treatment priming with ALA significantly increased the superoxide dismutase and peroxidase activities in the seedlings by 144% and 282%, respectively, as compared with the hydropriming treatment. Seed priming with ALA at 0.2 μg mL–1 significantly increased the relative growth rate of seedling and lowered seedling water content as compared with the values without priming or with hydropriming. Seed priming with ALA was confirmed to enhance rice seed germination capacity, seedling growth, and antioxidant enzyme activity in rice seedlings.

Characterization of synthetic ecdysteroid analogues as functional mimics of brassinosteroids in plant growth

Brassinosteroids (BRs) are plant steroidal hormones that play important roles in many stages of plant growth. Several plant species produce ecdysteroids, which are known as insect molting steroid hormones. In this study, we evaluated the biological activities of three hydroxysteroidal compounds, 20-hydroxyecdysone (ECD), 7,8-dihydro-8α-20-hydroxyecdysone (DHECD), and 7,8-dihydro-5α,8α-20-hydroxyecdysone (α-DHECD), and compared their activities with that of brassinolide (BL), the most potent BR. In rice, DHECD and α-DHECD enhanced the degree of lamina inclination, as do BRs. In Arabidopsis thaliana, DHECD and α-DHECD increased hypocotyl length in the wild-type, and also partially overcame the hypocotyl shortening in the wild-type caused by 0.3μM brassinazole, a specific BR biosynthesis inhibitor. DHECD and α-DHECD partially reduced dwarfism in the BR-biosynthesis-deficient mutant det2. Treatment with DHECD or α-DHECD downregulated the expression of the BR biosynthesis genes DWF4 and CPD, which are generally, suppressed by BR, and upregulated the expression of TCH4 and SAUR-AC1, which are generally promoted by BR. However, their regulated activities were less effective than BL. Moreover, the 10-4M DHECD and α-DHECD induced the accumulation of dephosphorylated BIL1/BZR1 that enhanced BR signaling as a master transcription factor. In contrast, ECD did not affect rice lamina bending, Arabidopsis hypocotyl elongation, the expression levels of BR-related genes and BIL1/BZR1 phosphorylation status. Based on these results, we hypothesize that both DHECD and α-DHECD have functional activities similar to those of BR.

QUANTIFICATION OF 5-AMINOLEVULINIC ACID IN SWINE MANURE EXTRACT BY HPLC-FLUORESCENCE

A modified high performance liquid chromatography (HPLC)-fluorescence method for determination of the 5-aminolevulinic acid (ALA) concentration in swine waste was studied. The method included digestion of the sample by heating in aqueous HCl and derivatization by acetyl acetone/formaldehyde reagent. The derivative was isolated and detected by fluorescence with excitation at 370 nm and emission at 460 nm. Chromatographic separation of ALA was carried out using the optimum mobile phase of a methanol/water/glacial acetic acid (49.5:49.5:1, v/v/v). The method produced a limit of detection of the ALA concentration of 0.10 µg/mL and a limit of quantification of the ALA concentration of 0.31 µg/mL. The method was used for determination of the ALA concentration in concentrated swine manure extract (CSME) fermented for 0, 7, 14, 21, and 28 d. The ALA concentrations in the CSME fermented for 0, 7, and 14 d were low and ranged from 0.216 to 0.399 µg/mL, but increased to a level ranging between 1.240 and 1.295 µg/mL at 21 and 28 d of fermentation. The results of the study confirmed the presence of ALA in the swine waste. The ability to quantify the ALA concentration in swine waste developed by the study was confirmed.

Improving photosynthetic performance and some fruit quality traits in mango trees by shading

Excess solar radiation under hot climate can lead to decline in photosynthetic activity with detrimental effects on growth and yield. The aim of this study was to evaluate the use of a transparent plastic roof as shading for diurnal changes in photosynthetic gas exchange, chlorophyll fluorescence, fruit set and quality of mango (Mangifera indica L.) cv. ‘Nam Dok Mai’ growth in the field conditions. Fully expanded leaves were examined either shaded by the plastic roof or sunlit under natural conditions. Leaf temperature and leaf-to-air vapour pressure deficit of the shaded leaves measured on the clear day were lowered compared to those of the sunlit leaves. It resulted in increased stomatal conductance and photosynthetic rates of the shaded leaves compared to those of the sunlit leaves, especially from the morning to midday. Furthermore, the reversible decrease of the maximal quantum yield of PSII was more pronounced in the sunlit leaves than that in the shaded ones. Shading increased the total fruit number; the shaded fruits developed better external color than that of the sun-exposed fruits. Our results indicated that shading could maintain the high photosynthetic activity by reducing stomatal limitations for carbon supply and was effective in alleviating the photoinhibitory damage to PSII during bright and clear days with excessive radiation. Finally, shading could increase the number of fruits and improve mango peel color.