The effects of salinity on ion concentrations within the root cells of Zea mays L

Bacillus aryabhattai enhanced proline content, stabilized membrane and improved growth of cowpea under NaCl-induced salinity stress

AIMS

Salinity stress affects the growth of cowpea particularly at the stages of seed germination and early vegetative growth. This study examined the potential of particular stress-tolerant rhizospheric bacteria to improve the growth of cowpea under conditions of salinity stress.

METHODS AND RESULTS

Two rhizobacillus genotypes, Bacillus filamentosus-C8 and Bacillus aryabhattai-C29 were evaluated for their potentials to protect cowpea under NaCl-induced salinity stress. At 200 mM of NaCl concentration, control (non-inoculated) cowpea was affected, C8 was not able to significantly (p ≤ 0.05) alleviate the effects of salinity stress on cowpea growth while C29 significantly (p ≤ 0.05) reduced leaf wilting, increased chlorophyll content and improved the growth of cowpea plant under stressed condition. Interestingly, C29 significantly (p ≤ 0.05) induced high proline content and stabilized membrane by loss of electrolytes.

CONCLUSION

Our results indicate that stabilized membrane and enhanced proline content by Bacillus aryabhattai-C29 supported the growth of cowpea under salinity stress condition.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study revealed that rhizospheric bacteria screened for salinity stress tolerant have potential to be used as an effective bioprotectant for sustainable growth of cowpea under salinity stress condition.

Sodium and chloride exclusion and retention by non-grafted and grafted melon and Cucurbita plants

The effects of grafting on Na and Cl(-) uptake and distribution in plant tissues were quantified in a greenhouse experiment using six combinations of melon (Cucumis melo L. cv. Arava) and pumpkin (Cucurbita maxima Duchesne×Cucurbita moschata Duchesne cv. TZ-148): non-grafted, self-grafted, melons grafted on pumpkins, and pumpkins grafted on melons. Total Na concentration in shoots of plants with pumpkin or melon rootstocks was <60 mmol kg(-1) and >400 mmol kg(-1), respectively, regardless of the scion. In contrast, shoot Cl(-) concentrations were quite similar among the different scion-rootstock combinations. Na concentrations in exudates from cut stems of plants with a pumpkin rootstock were very low (<0.18 mM), whereas those in the exudates of plants with melon rootstocks ranged from 4.7 mM to 6.2 mM, and were quite similar to the Na concentration in the irrigation water. Root Na concentrations averaged 11.7 times those in the shoots of plants with pumpkin rootstocks, while in plants with melon rootstocks, values were similar. Two mechanisms could explain the decrease in shoot Na concentrations in plants with pumpkin rootstocks: (i) Na exclusion by the pumpkin roots; and (ii) Na retention and accumulation within the pumpkin rootstock. Quantitative analysis indicated that the pumpkin roots excluded ∼74% of available Na, while there was nearly no Na exclusion by melon roots. Na retention by the pumpkin rootstocks decreased its amount in the shoot by an average 46.9% compared with uniform Na distribution throughout the plant. In contrast, no retention of Na could be found in plants grafted on melons.

Longitudinal and transverse profiles of K+ and Cl- concentration in 'low-' and 'high-salt' barley roots

The concentrations of K⁺ and Cl^- in meristematic and differentiated cells of barley (Hordeum Vulgare. L. ev. California Mariout) roots were determined by means of quantitative X-ray microanalysis. In roots of seedlings grown in 0.5 mM CaSO₄ ('low-salt' roots), the mean cytoplasmic K⁺ concentration of meristematic cells was 194 mM, while the average vacuolar concentrations at 10, 50 and 100 mm from the root tip were 62,25 and 22 mM, respectively. Such marked differences in vacuolar K⁺ concentration of differentiated cells were not found in roots of seedlings grown in full strength Johnson solution ('high-salt' roots). Thus the maintenance of K⁺ at a relatively high concentration in the cytoplasm of meristematic cells of 'low-salt' roots appears to be a priority requirement. The mean Cl^- concentration in the cytoplasm of meristematic cells of 'low-salt' roots was 4.6 mM, and the vacuolar Cl^- concentration declined towards the root base. These measured concentrations are compatible with previous data, indicating that X-ray microanalysis of fully-hydrated samples, used together with colloidal graphite mixtures as standards, provides a reliable means of measuring ion concentrations at the subcellular level.

QUNTITATIVE ION DISTRIBUTION WITHIN ROOT CELLS OF SALT-SENSITIVE AND SALT-TOLERANT MAIZE VARIETIES

Significant varietal differences were apparent in the survival of seedlings of maize in saline conditions but only at relatively high external concentrations (200 mol m^-3 NaCl), where there was a range from 0 to 66% survival, 25 d after salinization. For the varieties examined there was a strong negative correlation between Na concentrations in the third leaf and survival. Two resistant varieties (Across 8024 and Protador) and one salt-sensitive variety (LG₁₁ ) were identified. The characteristics of ion accumulation were clearly different in salt-tolerant and salt-sensitive types, the difference becoming more pronounced with plant age. The distribution of ions, particular those of Na, K and Cl, was determined within subcellular compartments of roots cells using X-ray microanalysis of freeze-substituted tissue. Salinity induced a greater increase (about 1.7 times) in cytoplasmic Na concentration in the salt-sensitive variety (LG₁₁ ) than in resistant varieties (Across 8024 or Protador). The mean K:Na ratio in the cytoplasm of the root cortical cells in the salt-resistant varieties grown for 15 d in saline conditions (100 mol m^-3 NaCl) was twice that found for LG₁₁ . Sodium and Cl concentrations in the vacuoles decreased radially inwards from the epidermal cells in salt-treated roots of LG₁₁ .