No abstract

Occasionally, wheat can be exposed to overnight freezing temperatures whilst it is in the early reproductive stage and considerable frost damage can occur. In the vegetative stage, full expression of frost tolerance genes can be gained when plants are exposed to acclimation temperatures (4 °C). Paradoxically, wheat during flowering has limited or no ability to effectively acclimate or re‐acclimate and it demonstrates frost sensitivity during this stage. Using a combined approach involving infrared thermography and molecular analysis, the causes and effects of frost‐induced damage to wheat during ear emergence were investigated. It was demonstrated that frost damage only occurs to wheat ears if the temperature falls below −5 °C but some ears, and some spikelets on frozen ears do not freeze but supercool and escape freezing. In whole plant freezing experiments, spikelets showed both complete and partial sterility upon maturation and this was linked to parallel infrared observation of detached ears showing full or partial freezing of spikelets. It was hypothesised that wherever spikelet freezing occurred the spikelet was sterile and grain production per ear was drastically reduced, and in contrary, spikelet survival was as a result of supercooling. Molecular analysis of the upregulation of Cbf14 showed that as ear emergence progressed the ability to induce Cbf14 decreased but at early stages of ear emergence Cbf14 was able to be induced by exposure to acclimating temperatures (4 °C). The hypothesis that the lack of the ear to acclimate is because of the incapability to induce the CBF transcription factor was only partially upheld in this investigation. Further work is needed to elucidate more precisely the molecular incompetency for the acclimation of wheat during ear emergence.

Polyethylene glycol (PEG) can be used in somatic embryogenesis to enhance embryogenic development and improve the success of in vitro culture but PEG also causes osmotic stress in developing embryos. The effects of PEG on embryo growth and development in date palm cell suspension culture and associated antioxidant enzyme activities were evaluated. Callus maintained on MS basal media was transferred to regeneration liquid media supplemented with increasing levels (0-20%) of polyethylene glycol 6000 (PEG) to induce osmotic stress. The degree of embryogenic callus formation, its fresh weight, and the percentage of normal embryo callus shapes were increased with an increase in the level of PEG up to 10%. Total soluble protein (TSP), proline, glycine betaine (GB), total soluble phenol (TSPh), total sugars (TS), and total soluble organic acids (TOA) also increased whereas superoxide dismutase (SOD) activity decreased in response to PEG supplementation. Raising the PEG level increased malondialdehyde (MDA) concentration up to 10% PEG and thereafter decreased. Glutathione reductase (GR) and catalase (CAT) activities decreased at the highest levels of PEG. The proportion of normal embryo developmental shapes were about 50% compared with 20% abnormal shapes at optimum levels of PEG. Proliferation of somatic embryos was influenced by their developmental shapes. Cv. Samani accumulated more organic solutes compared with cv. Sewi in both control and stress inducing media. In contrast, lipid peroxidation, GR, SOD, and CAT activities were significantly higher in cv. Sewi than in cv. Samani indicating that the cv. Samani had the ability to tolerate a higher level of osmotic stress compared to cv. Sewi due to the enhanced osmotic rebalancing within its tissues.

Drought stress is one of the most harmful factors of plant growth and productivity. Two pot experiments were carried out at greenhouse of agriculture botany department, faculty of agriculture, zagazig university, Sharkya Governorate, Egypt, during two successive winter seasons (2014/2015 and 2015/2016), to study the role of proline or potassium in mitigation the harmful impact of drought stress conditions on wheat plants c.v Misr 2 grown in Egypt. Growth parameters, yield and biochemical constituents were evaluated.Results show that all plant growth characters studied (shoot dry weight, leaf area and plant height) as well as yield and its components (dry weight of grains /plant, number of spikes/plant, number of grains/plant, number of grains/ spike, and1000-grains weight) were decreased with increasing irrigation intervals (irrigation every 10, 20 and 30 days) during the two successive growing seasons.The most effective treatment was Irrigation every 30 days in decreasing yield and its components. Integrated application of proline or potassium at rate of 0.1 and 0.2 % alleviated these negative effects by enhancing the growth and productivity. However, these increases were less than the control treatment. Moreover, it was found that drought stress decreased RWC, ELWR, RWL, photosynthetic pigments contents, whilst increasing, total phenol, proline as well as peroxidase and catalase activities in the leaves of wheat plants during the two growing seasons. However, application of proline or potassium increased all these parameters and decreasing total phenols. Treatment of proline at rate of 0.2 % was the most effective in this respect. It is recommended that application of proline or potassium can fully or partially counteract the adverse effect of drought stress on growth, and productivity of wheat plants through their effects on biochemical constituents

Salinity is destructive factor and one of various abiotic stresses which strongly affects crop productivity and limits marketable yield of vegetable crops, for example pepper plants. This work studied the effects of sole application of each of Humic Acid (HA) and Arbuscular Mycorrizal Fungi (AMF), Glomus fasciculatum inoculation and their combinations in order to reduce the harmful effects of salinity stress on growth, yield and endogenous bio-constituents in pepper cultivar top star. Growth parameters at 75 days after transplanting and yield components were decreased under levels of salt stress (2000 or 4000 ppm). Applied of humic acid and mycorrhizae, partially counteracted the harmful effects of salinity stress levels. By increasing salt stress levels, proline, peroxidase and catalase activities and Na content were increased, but photosynthetic pigments in leaves and N, P, K content in shoots of pepper plants were decreased. In addition, all treatments of humic acid and mycorohizae either alone or in combination under different salt stress levels, slightly increased the content of proline, N, P, K and photosynthetic pigments, peroxidase and catalase activities while, Na content was decreased in pepper plants. It was observed that, the interaction between humic acid and mycorohizae increased the positive effect of mycorohizae inoculation. Results indicated also that, mycorrhizal inoculation help in ameliorating the damage caused by salt stress conditions in pepper plants. Application of humic acid combined with mycorrhizae, promote much more plant growth. These results provide support for the field application of humic acid and mycorrhizae to decline the harmful effects of salty soils.