Water relations, short-chain oligosaccharides and rheological properties in lettuces subjected to limited water supply and low temperature stress

- Higher apparent viscosity and solute content in severe water deficit lettuces.
- Short-chain fructooligosaccharides induction by moderate water reduction in lettuces.
- Moderate water limitation reduces senescence-related changes in growing lettuces.
- Severe water reduction avoids raffinose accumulation after low temperature stress.
- Water status in lettuces subjected to water deficit and low temperatures stress.

Reducing water consumption and increasing the quality of vegetables is a particularly high priority in agricultural production. Thus, we set out to analyze the effect of restricting the water supply on water relations, rheological properties, and the accumulation of solutes and protective fructooligosaccharides (FOS) and raffinose family compounds (RFOs) in lettuces grown under controlled greenhouse conditions. In addition, we analyzed whether water restriction can prevent senescence-related changes and overcome the stress imposed by subsequent exposure to low temperature. Lettuces var. Maravilla de Verano were grown under three different water supply regimes, well-watered (WW), moderate water deficit (MWD) and severe water deficit (SWD). Our results indicate that accumulated transpiration (AT) was higher in WW plants than in lettuces subjected to water deficit. The relative water content (RWC) was significantly influenced by a restricted water supply but not by additional low temperature stress. Water deficit caused a significant decrease in the amount of unfreezable water (Uw), determined calorimetrically, in association with a significant decrease in total water content (TW). After the additional low temperature stress, there was no further drop in Tw, although a significant decrease in Uw was evident, mainly in SWD lettuces. A moderate water deficit enhanced nystose and kestopentaose accumulation. After imposing low temperature stress, MWD lettuces had a lower apparent viscosity, concomitant with an increase in firmness, fewer senescence-related changes and a sharp increase in raffinose. We conclude that moderate water limitation, improving the endogenous levels of FOS and reducing the cleavage of wall polysaccharides backbones, thus reducing viscosity and increasing firmness, could be useful to retain water inside cells, avoiding quality loss and increasing the capacity of the lettuce to resist low non-freezing temperatures.