Effects of drought stress on growth, solute accumulation and membrane stability of leafy vegetable, huckleberry (Solanum scabrum Mill.).

The present study sought to investigate the factors implicated in growth impairment of huckleberry (a leafy vegetable) under water stress conditions. To achieve this, seedlings of plant were subjected to control, mild stress and severe stress conditions for 30 days. Plant growth, plant water relation, gas exchange, oxidative stress damage, electrolyte leakage rate, mineral content and osmolyte accumulation were measured. Water deficit markedly decreased leaf, stem and root growth. Leaf photosynthetic rate was tremendously reduced by decrease in stomatal conductance under stress conditions. Malondialdehyde (MDA) content markedly increased under mild (82%) and severe (131%) stress conditions, while electrolyte leakage rate (ELR) increased by 59% under mild stress and 3-fold under severe stress. Mineral content in leafwas high in stressed plants, while proline content markedly increased under mild stress (12-fold) and severe stress (15-fold), with corresponding decrease in osmotic potential at full turgor and an increase in osmotic adjustment. These results suggest that maintenance of high mineral content and osmotic adjustment constitute important adaptations in huckleberry under water deficit conditions and that growth depression under drought stress would be mainly caused by increased electrolyte leakage resulting from membrane damage induced by oxidative stress.

Phytate degradation by fungi and bacteria that inhabit sawdust and coffee residue composts.

Phytate is the primary source of organic phosphorus, but it cannot be directly utilized by plants and is strongly adsorbed by the soil, reducing bioavailability. Composting is a process used to improve the bioavailability of phytate in organic wastes through degradation by microorganisms. In this study, we aimed to investigate the phytate-degrading ability of fungi and bacteria that inhabit sawdust compost and coffee residue compost, and their contribution to the composting process. In the plate assay, the fungi that formed clear zones around their colonies belonged to the genera Mucor, Penicillium, Galactomyces, Coniochaeta, Aspergillus, and Fusarium, while the bacteria belonged to the genera Pseudomonas, Enterobacter, Chitinophaga, and Rahnella. Eight fungal isolates (genera Mucor, Penicillium, Galactomyces, and Coniochaeta) and four bacterial isolates (genera Pseudomonas, Enterobacter, and Rahnella) were selected to evaluate phytase activity in their liquid culture and their ability to degrade phytate in organic materials composed of mushroom media residue and rice bran. The selected fungi degraded phytate in organic materials to varying degrees. Penicillium isolates showed the highest degradation ability and Coniochaeta isolate exhibited relatively high degradation ability. The clear zone diameters of these fungal isolates displayed significantly positive and negative correlations with inorganic and phytate phosphorus contents in the organic materials after incubation, respectively; however, none of the selected bacteria reduced phytate phosphorus in organic materials. It is therefore possible that fungi are major contributors to phytate degradation during composting.

Isolation and characterization of cellulose-decomposing bacteria inhabiting sawdust and coffee residue composts.

Clarifying the identity and enzymatic activities of microorganisms associated with the decomposition of organic materials is expected to contribute to the evaluation and improvement of composting processes. In this study, we examined the cellulolytic and hemicellulolytic abilities of bacteria isolated from sawdust compost (SDC) and coffee residue compost (CRC). Cellulolytic bacteria were isolated using Dubos mineral salt agar containing azurine cross-linked (AZCL) HE-cellulose. Bacterial identification was performed based on the sequence analysis of 16S rRNA genes, and cellulase, xylanase, ß-glucanase, mannanase, and protease activities were characterized using insoluble AZCL-linked substrates. Eleven isolates were obtained from SDC and 10 isolates from CRC. DNA analysis indicated that the isolates from SDC and CRC belonged to the genera Streptomyces, Microbispora, and Paenibacillus, and the genera Streptomyces, Microbispora, and Cohnella, respectively. Microbispora was the most dominant genus in both compost types. All isolates, with the exception of two isolates lacking mannanase activity, showed cellulase, xylanase, ß-glucanase, and mannanase activities. Based on enzyme activities expressed as the ratio of hydrolysis zone diameter to colony diameter, it was suggested that the species of Microbispora (SDCB8, SDCB9) and Paenibacillus (SDCB10, SDCB11) in SDC and Microbispora (CRCB2, CRCB6) and Cohnella (CRCB9, CRCB10) in CRC contribute to efficient cellulolytic and hemicellulolytic processes during composting.