Sodium sensing induces different changes in free cytosolic calcium concentration and pH in salt‐tolerant and ‐sensitive rice (Oryza sativa) cultivars

Abstract

Perception of salt stress in plant cells induces a change in the free cytosolic Ca2+, [Ca2+]cyt, which transfers downstream reactions toward salt tolerance. Changes in cytosolic H+ concentration, [H+]cyt, are closely linked to the [Ca2+]cyt dynamics under various stress signals. In this study, salt‐induced changes in [Ca2+]cyt, and [H+]cyt and vacuolar [H+] concentrations were monitored in single protoplasts of rice (Oryza sativa L. indica cvs. Pokkali and BRRI Dhan29) by fluorescence microscopy. Changes in cytosolic [Ca2+] and [H+] were detected by use of the fluorescent dyes acetoxy methyl ester of calcium‐binding benzofuran and acetoxy methyl ester of 2′, 7′‐bis‐(2‐carboxyethyl)‐5‐(and‐6) carboxyfluorescein, respectively, and for vacuolar pH, fluorescent 6‐carboxyfluorescein and confocal microscopy were used. Addition of NaCl induced a higher increase in [Ca2+]cyt in the salt‐tolerant cv. Pokkali than in the salt‐sensitive cv. BRRI Dhan29. From inhibitor studies, we conclude that the internal stores appear to be the major source for [Ca2+]cyt increase in Pokkali, although the apoplast is more important in BRRI Dhan29. The [Ca2+]cyt measurements in rice also suggest that Na+ should be sensed inside the cytosol, before any increase in [Ca2+]cyt occurs. Moreover, our results with individual mesophyll protoplasts suggest that ionic stress causes an increase in [Ca2+]cyt and that osmotic stress sharply decreases [Ca2+]cyt in rice. The [pH]cyt was differently shifted in the two rice cultivars in response to salt stress and may be coupled to different activities of the H+‐ATPases. The changes in vacuolar pH were correlated with the expressional analysis of rice vacuolar H+‐ATPase in these two rice cultivars.

Cytosolic calcium and pH signaling in plants under salinity stress

“…However, it has been suggested that the SOS1 protein, which has a long C-terminal tail residing in the cytosol, might sense Na + . 24,26,56 Kader et al 38 showed that Na + must enter into the cytosol to be sensed in rice protoplasts, which is consistent with the earlier suggestion that the SOS1 protein might sense Na + inside the cytosol. On the other hand, for the halophytic plant quince it was shown that Na + entry into the cell may not be necessary for cytosolic Ca 2+ elevation.…”

“…11,[38][39][40][41][42]57,[61][62][63][64] From the results so far, it can be concluded that the change in [Ca 2+ ] cyt is not uniform and varies with species, cell type or tissue type. 38,39,43,57,59 It can also be considered that the specific Ca 2+ signatures (the increase with different amplitudes and their maintenance of a low cytosolic Na + /K + ratio is also critical for the function of cells. 16,17 Tolerance mechanisms to salinity stress.…”

“…The measurement of changes in [Ca 2+ ] cyt under high salinity stress has been performed by using different techniques, such as fluorescence microscopy measurements in root hairs, 37 in individual mesophyll protoplast 38,39 and in intact whole plant by using aequorin luminescence. [40][41][42][43] A number of studies also reported changes in pH cyt in different plant species under salinity stress, which seem to vary between salinity sensitive and tolerant species.…”

Exogenous application of plant growth regulators induce chilling tolerance in direct seeded super and non-super rice seedlings through modulations in morpho-physiological attributes

“…Calcium chloride, humic substances, salicylic acid and brassinosteroids are considered as plant endogenous regulators in defending stress (Kader et al 2007;Kader and Lindberg 2010). Brassinosteroids, well-known natural substances which modulate plant growth by improving its tolerance under stress (Anjum et al 2011b).…”

“…Individual or separate application of different PGRs induced modulations in plant response to various abiotic stresses has been widely reported (Kader et al 2007;Anjum et al 2011b), however, their integrated application and eventual effects on germination behavior and seedling development of direct seeded super and non-super rice under low temperature is still elusive. This study was therefore designed with the objectives of investigating the germination potential and relative performance of direct seeded super and non-super rice seedlings under low temperature (11 °C to 15 °C) to find out the critical temperature for rice seed germination and to study the possible roles of PGRs in stress alleviation.…”