Excess fluoride (F − ) inhibits the growth and metabolism of several crop plants, while some have an innate ability for F − tolerance. The present study was undertaken to explain how plants tolerate F − toxicity and understand the efficacy of exogenous stress protectants and phytoremediation approaches for F − homeostasis and tolerance of crop plants. This review comprehends existing information available so far on the F − accumulation toxicity and tolerance mechanisms. A high level of F − inhibits plant growth, water and nutrition uptake, enzyme activity, and yield. This review concludes that plants tolerate through F − homeostasis (exclusion, chelating, and compartmentalization) and gene activation for enhanced pathways of antioxidants, hormones, osmolytes, stress proteins, transporters, and metabolites. Exogenously applied stress protectants like salicylic acid (SA), polyamines (PAs), melatonin (Mel), glycine betaine, calcium (Ca 2+ ), and nanoparticles are differentially effective in reducing F − accumulation and toxicity by regulating various pathways. Application of minerals minimizes the F − accumulation through changing pH of soil, chelate formation with F − , and permeability of the cell membrane. Although many of the physiological aspects (enzyme activities, F − accumulation and regulation) were studied earlier, however, an effort has been made for the first time to understand the genetic basis and role of stress protectants and mineral nutrition, regulating these physiological activities, and explore new integrated approaches related to F − mitigation by means of phytoremediation. This review covers the recent development in F − transporters, gene expression, and biochemical and hormonal levels which could be utilized in regulating F − toxicity through omics and transgenic approaches in the future.

Sewan (Lasiurus sindicus Henr.) is an endemic fodder grass of low rainfall sandy habitat of hot Indian Thar desert. To understand drought responses and tolerance mechanism in Lasiurus sindicus, seedling growth, root cell viability, changes in enzymatic antioxidants and oxidative injury were assayed at early stage of seedlings in polyethylene glycol (PEG) 6000 (5, 10 and 20%)-induced drought stress. The reduction of seed germination, seedling growth, relative water content and vigor index was found with high level of PEG (10-20%), while 5% PEG slightly increased the germination and the growth parameters. A decline in pigments (Chl a, Chl b, total Chl, carotenoids), chlorophyll stability index, membrane stability index and protein content was observed, which was correlated with increased level of malondialdehyde, an indicator of excess reactive oxygen species. Results showed that increasing level of PEG activated the antioxidative enzymes, superoxide dismutase, peroxidase and catalase. Non-enzymatic antioxidants (ascorbate, phenols) and accumulation of cytosolutes (proline and sugar) for regulation of growth, osmotic potential and reactive oxygen species in drought tolerance. Overall results showed that seeds have adaptive mechanisms for germination and growth under lower level of drought, while increasing drought stress reduced growth potential of L. sindicus. It exhibited drought tolerance features, enhancement in activity of antioxidative enzyme and cytosolutes accumulation which involved in regulation of oxidative damage and osmotic adjustment for survival of the seedlings. Furthermore, our results provide important information about the physiological and antioxidative responses of the seedlings and mechanism associated with drought tolerance of L. sindicus.

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In a pot experiment, BAU-Biofungicide (Trichoderma harzianum) neem oil and  curaterr (carbofuran) 5G were tested against root-knot (Meloidogyne javanica)  of two papaya varieties Kashempuri and Deshi papaya. Seedlings were  inoculated with second stage larvae of M. javanica. Neem oil (5 ml/ 10g seeds)  and BAU-Biofungicide (1:4) were used as seed treatant and curaterr as side  dressing. Both the bio-agents significantly increased the root and shoot growth  of papaya plant and reduction of galls and eggmasses and suppressed the  development of J2, J3, and J4 and adult females of M. javanica. Efficacy of  BAU-Biofungicide was to reduce the gall and nematode development and to  increase plant growth was similar to nematicide curaterr. BAU-Biofungicide  gave higher effect in most of the growth characters compared to neem oil and  prevented the development of adult females and juveniles like nematicide  curaterr. DOI: http://dx.doi.org/10.3329/bjar.v37i2.11230 Bangladesh J. Agril. Res. 37(2): 271-277, June 2012

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