| Abstrakt: |
Soil salinity imposes severe stress on plant growth and limits crop yield, while humic acids (HA) promote plant growth and mitigate different abiotic stresses. HA has auxin-like activity, but the involvement of ethylene signaling in their action is poorly investigated. Moreover, whether the mitigating action of HA in the salt stress responses depends on ethylene is unclear. Thus, this work aimed to investigate whether (i) the humic substances mitigate the effects of salt stress on cultivated tomatoes and (ii) the action of humic acids depends on ethylene perception. To do that we used a genetic approach through wild-type (WT) MICRO-TOM (Solanum lycopersicum) and the ethylene insensitive Never ripe (Nr) mutant. Our data showed that HA promotes root growth of WT and Nr plants. The number of lateral roots, the main morphological marker of HA activity, decreased respectively, 33% and 18%, in WT and Nr plants under NaCl alone, while HA alone stimulated them in 7% (in WT) and 12% (in Nr), both compared to control conditions. The inhibitory effect of salt stress on the number of lateral roots was not observed when WT and Nr plants were simultaneously treated with HA and NaCl (HA + NaCl) which was significantly equal to those under control conditions. HA activity also mitigates the inhibitory effects of salt stress on photosynthesis of WT and Nr plants. Specifically, compared to the control, the relative chlorophyll content increased about 1.77 and 2.44 times, respectively, in WT and Nr plants in the HA + NaCl combination. Moreover, the increase in light absorption capacity was followed by increased photosystem II quantum yield and non-photochemical exciton quenching. Therefore, photochemical analysis demonstrated that HA promotes photosynthetic activity and reduces photodamage, in either unstressed or salt-stressed plants, and either WT or Nr plants. Overall, through a genetic approach, our data demonstrated that HA promotes plant growth independent of ethylene perception, as well as mitigates the inhibitory effects of salt stress. [ABSTRACT FROM AUTHOR] |
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