Leaf Soluble Sugars and Free Amino Acids as Important Components of Abscisic Acid—Mediated Drought Response in Tomato

Abstract

Water deficit has a global impact on plant growth and crop yield. Climate changes are going to increase the intensity, duration and frequency of severe droughts, particularly in southern and south-eastern Europe, elevating the water scarcity issues. We aimed to assess the contribution of endogenous abscisic acid (ABA) in the protective mechanisms against water deficit, including stomatal conductance, relative water potential and the accumulation of osmoprotectants, as well as on growth parameters. To achieve that, we used a suitable model system, ABA-deficient tomato mutant, flacca and its parental line. Flacca mutant exhibited constitutively higher levels of soluble sugars (e.g., galactose, arabinose, sorbitol) and free amino acids (AAs) compared with the wild type (WT). Water deficit provoked the strong accumulation of proline in both genotypes, and total soluble sugars only in flacca. Upon re-watering, these osmolytes returned to the initial levels in both genotypes. Our results indicate that flacca compensated higher stomatal conductance with a higher constitutive level of free sugars and AAs. Additionally, we suggest that the accumulation of AAs, particularly proline and its precursors and specific branched-chain AAs in both, glucose and sucrose in flacca, and sorbitol in WT, could contribute to maintaining growth rate during water deficit and recovery in both tomato genotypes.

Differential Response of Two Tomato Genotypes, Wild Type cv. Ailsa Craig and Its ABA-Deficient Mutant flacca to Short-Termed Drought Cycles

“…The accumulation of osmolytes under drought is considered as a key protective mechanism against water stress in plant cells. In our previous work with the same tomato genotypes, we demonstrated that the extent of drought-induced accumulation of proline was similar in WT and flacca, irrespective of differences in their constitutive ABA levels [51]. However, when plants were grown under higher light intensity, drought induced more than three times higher accumulation of proline in WT than in flacca.…”

“…Recently, we reported that the same flacca mutant exhibited constitutively higher levels of soluble sugars and free amino acids (AAs) compared with its parent line Ailsa Craig cv. [51]. Here, we analyze the drought effects on plants by imposing more natural conditions on our model system that would allow maximal photosynthetic rates and faster growth.…”

Responsiveness of Early Response to Dehydration Six-Like Transporter Genes to Water Deficit in Arabidopsis thaliana Leaves

“…In the MD phase, WC decreased from 92.2 to 90% (i.e., a net 2.2% water loss), thereby reaching a cumulative water loss of 8%, which caused stomatal closure as an early plant response to maintain the plant water state under reduced soil water potential (Costa França et al, 2000;Flexas et al, 2004;Blouin et al, 2007;Harb et al, 2010;Arve et al, 2011). ABA is known as the major plant hormone with a double function involved not only in stomatal closure, but also in the prevention of stomatal opening (Liu et al, 2005;Seki et al, 2007;Arve et al, 2011;Živanović et al, 2020). The steps that occur between the sensing of drought and the production of ABA are complex vary among plant species FIGURE 8 | Expression level of AtESL1.02/ERDL6, AtESL3.03, AtESL3.05/ESL3, and AtESL3.07/ESL1 in the leaves of T-DNA insertional mutants: atesl1.02/erdl6, atesl3.03, atesl3.05/esl3, and atesl3.07/esl1.…”

Distribution of polyphenolic and sugar compounds in different buckwheat plant parts

“…11,18,19 A high content of sucrose in the leaf sample extract, as well as the low F/G ratio (Table 1), could also be a consequence of some kind of plant stress. 9 Considering that the high content of sucrose in the buckwheat leaf extract sample (Table 1) takes the amount of $30% of total sugars in this extract, it was comparable to the quantied sucrose content in the leaf sample of cucumber plant under the cold stress. 7 Furthermore, Taiz et al 4 reported that an increase in sucrose content was associated with an increase in cold tolerance.…”