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Salinity is one of the major constraints in oilseed rape (Brassica napus L.) production. One of the means to overcome this constraint is the use of plant growth regulators to induce plant tolerance. To study the plant response to salinity in combination with a growth regulator, 5-aminolevulinic acid (ALA), oilseed rape plants were grown hydroponically in greenhouse conditions under three levels of salinity (0, 100, and 200 mM NaCl) and foliar application of ALA (30 mg/l). Salinity depressed the growth of shoots and roots, and decreased leaf water potential and chlorophyll concentration. Addition of ALA partially improved the growth of shoots and roots, and increased the leaf chlorophyll concentrations of stressed plants. Foliar application of ALA also maintained leaf water potential of plants growing in 100 mM salinity at the same level as that of the control plants, and there was also an improvement in the water relations of ALA-treated plants growing in 200 mM. Net photosynthetic rate and gas exchange parameters were also reduced significantly with increasing salinity; these effects were partially reversed upon foliar application with ALA. Sodium accumulation increased with increasing NaCl concentration which induced a complex response in the macro-and micronutrients uptake and accumulation in both roots and leaves. Generally, analyses of macro-(N, P, K, S, Ca, and Mg) and micronutrients (Mn, Zn, Fe, and Cu) showed no increased accumulation of these ions in the leaves and roots (on dry weight basis) under increasing salinity except for zinc (Zn). Foliar application of ALA enhanced the concentrations of all nutrients other than Mn and Cu. These results suggest that under short-term salinity-induced stress (10 days), exogenous application of ALA helped the plants improve growth, photosynthetic gas exchange capacity, water potential, chlorophyll content, and mineral nutrition by manipulating the uptake of Na + .

This study suggests that Ca(2+) in the proximity of plasma membrane is proficient in alleviating Cd toxicity by reducing the cell-surface negativity and competing for Cd(2+) ion influx. Consequently, both the plant growth and activity of diurnal photosynthetic system remain the least altered under Cd-provoked toxicity stress.

In the present study, the roles of foliarly applied 5-aminolevulinic acid (ALA) in photosynthetic parameters, ion contents and expression of several photosynthetic genes were investigated in rapeseed (Brassica napus L.) under well watered and drought conditions. Drought stress reduced relative plant growth rate and leaf water content (RWC), and contents of photosynthetic pigments, starch, soluble proteins and ions in roots. This type of stress, however, stimulated the accumulation of soluble sugars and free amino acids, as well as leaf proline contents. The transcript levels of photosynthetic genes were also down-regulated under drought stress. Exogenously applied ALA partially reduced growth inhibition and increased RWC and chlorophyll contents under drought conditions. The expression of photosynthetic genes was induced by ALA under both normal and drought conditions, which may contribute to an increased photosynthetic capacity. The ALA application further improved the accumulation of hexose and sucrose, accompanied by the maintenance of starch contents in the leaves and possibly relatively higher RWC under drought stress. Based on these results, we suggest that ALA promotes plant growth under drought stress via improving photosynthetic assimilation, increasing chlorophyll content and inducing the expression of several photosynthetic genes. ARTICLE HISTORY

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