Chlorophyll (Chl) fluorescence is a subtle reflection of primary reactions of photosynthesis. Intricate relationships between fluorescence kinetics and photosynthesis help our understanding of photosynthetic biophysical processes. Chl fluorescence technique is useful as a non-invasive tool in eco-physiological studies, and has extensively been used in assessing plant responses to environmental stress. The review gives a summary of some Chl fluorescence parameters currently used in studies of stress physiology of selected cereal crops, namely water stress, heat stress, salt stress, and chilling stress.

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Growth analysis indicated that carbon gain in the alpine succulent Sedum album tended to take place early during the growing season. Leaf water potential remained unchanged for a considerable length of time after the imposition of water stress in the field. Induction of crassulacean acid metabolism (CAM) by protracted water stress occurred before any signs of stress could be observed in the leaves, and appeared to be influenced by a complex interaction of environmental conditions including temperature and duration of sunshine. Increased levels of proline and betaine towards the end of the growing season appeared to reflect seasonal changes.

Background: The aim of the current study based on the production and characterization of exopolysaccharides (EPSs) isolated from marine sediment of the Mediterranean and Red Seas is to study its cytotoxic activity against HepG2 cells. Results: Eleven isolates have the ability to produce EPSs and also decreased the viability of HepG2 cell line in different manners. The five most promising isolates that produce high yield of EPSs and high cytotoxicity were identified by 16S RNA as Brevundimonas subvibrioides MSA1, Bacillus thuringiensis E4, Bacillus amyloliquefaciens MGA2, Pseudomonas fluorescens SGA3, and Advenella Kashmirensis NRC-7. The chemical composition of the following EPSs (M1, M3, M6, M15, M19, E2, E4, E10, S5, S7, and S11) demonstrates that they are acidic sulfated heteropolysaccharides with different relative ratios of monosugars of glucose, mannose, galactose, glucouronic acid, and mannouronic acid. The average molecular weights from 1.94 × 10 4 to 7.95 × 10 5 g/mol and the number average molecular weight from 1.51 × 10 4 to 7.53 × 10 5 g/mol. FTIR spectrum of the five EPSs indicated the presence of sulfate and carboxylic groups in different percentages. Conclusions: The EPSs produced from marine bacteria are very promising for treating the HepG2 cells.

The present paper reports the first record of the aquatic monocotyledon plant Wolffiella hyalina (Delile) Monod (Lemnaceae) in Saudi Arabia. The species was cited floating on the surface of rainwater-filled deep mountain pools at Sala Mountain south west of Saudi Arabia. This species has previously only been cited in Africa and India. The present citation, therefore, can be regarded as an addition to the flora of Saudi Arabia.

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