Abstract
BackgroundAbiotic stresses (e.g., heat or limited water and nutrient availability) limit crop production worldwide. With the progression of climate change, the severity and variation of these stresses are expected to increase. Exogenous silicon (Si) has shown beneficial effects on plant growth; however, its role in combating the negative effects of heat stress and their underlying molecular dynamics are not fully understood.ResultsExogenous Si significantly mitigated the adverse impact of heat stress by improving tomato plant biomass, photosynthetic pigments, and relative water content. Si induced stress tolerance by decreasing the concentrations of superoxide anions and malondialdehyde, as well as mitigating oxidative stress by increasing the gene expression for antioxidant enzymes (peroxidases, catalases, ascorbate peroxidases, superoxide dismutases, and glutathione reductases) under stress conditions. This was attributed to increased Si uptake in the shoots via the upregulation of low silicon (SlLsi1 and SlLsi2) gene expression under heat stress. Interestingly, Si stimulated the expression and transcript accumulation of heat shock proteins by upregulating heat transcription factors (Hsfs) such as SlHsfA1a-b, SlHsfA2-A3, and SlHsfA7 in tomato plants under heat stress. On the other hand, defense and stress signaling-related endogenous phytohormones (salicylic acid [SA]/abscisic acid [ABA]) exhibited a decrease in their concentration and biosynthesis following Si application. Additionally, the mRNA and gene expression levels for SA (SlR1b1, SlPR-P2, SlICS, and SlPAL) and ABA (SlNCEDI) were downregulated after exposure to stress conditions.ConclusionSi treatment resulted in greater tolerance to abiotic stress conditions, exhibiting higher plant growth dynamics and molecular physiology by regulating the antioxidant defense system, SA/ABA signaling, and Hsfs during heat stress.
Highlights
The results showed that exogenous Si application significantly increased shoot length under normal and heat stress conditions compared to –Si (36 and 31%, respectively; P < 0.001; Fig. 1a)
Shoot biomass significantly increased in +Si plants under normal and heat stress conditions compared to the results for –Si plants (61 and 70%, respectively; P < 0.001; Fig. 1b; Supplementary Fig. S1A)
+Si application significantly improved the root morphological traits and increased root length compared to the levels in –Si plants under heat stress and normal conditions (41 and 62%, respectively; P < 0.001; Fig. 1e), as shown by the secondary and tertiary root development
Summary
Abiotic stresses (e.g., heat or limited water and nutrient availability) limit crop production worldwide. It is predicted that a global temperature increase of 3–4 °C would cause a 15–35% reduction in crop productivity [3]. When plants experience heat stress, they undergo morphophysiological, biochemical, phytohormonal, and transcriptional changes such as osmotic imbalance, enzyme inactivation, reactive oxygen species (ROS) overproduction, and organelle damage, which can lead to cell death [2, 6, 7]. With the predicted increase in the frequency and intensity of heat stress, the rate osmotic potential is significantly hindered by the creation of a cell water potential imbalance, causing tissue damages and influencing essential biochemical pathways. To survive under varying temperature conditions, plants have evolved multiple internal tolerance strategies, such as the secretion of heat shock proteins (HSPs), changes in phytohormone levels, and the scavenging of ROS by different oxidation-reduction enzymes [5]. Improving crop stress tolerance is deemed an important undertaking in developing eco-friendly agricultural approaches
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