Influence of salinity on pip gene expression in citrus roots and its relationship with root hydraulic conductance, transpiration and chloride exclusion from leaves

Abstract

The present work studies the effect of salinity on PIP aquaporins gene expression in citrus roots and its relationship with root hydraulic conductance (Kr), transpiration rate (E) and chloride transport to leaves. To this end, ten-month-old seedlings of Cleopatra mandarin (CM), Carrizo citrange (CC) and Poncirus trifoliata (PT) were tested.No effect was detected of salt treatments on PIP1 and PIP2 aquaporin mRNA transcript abundances from citrus roots, although PIP1 expression in CM roots was lower than in CC and PT.The lowest Kr and E values were detected in CM, whereas PT had the highest. CC seedlings presented intermediate values for these parameters. Addition of HgCl2 to either control or salt solution (200mM NaCl) led to a decrease in Kr and E, thus implying aquaporin involvement. By contrast, salinity strongly reduced Kr and E in all plants, with this effect being unrelated to aquaporin activity.In salinized seedlings, E values appear to be related with Cl− concentration in leaves. Thus, CM seedlings treated with 80mM NaCl presented a lower Cl− uptake by leaves than PT, whereas this trend was intermediate in CC. Moreover, Hg2+ treatments significantly reduced leaf Cl− concentration in salt stressed plants, probably through the reduction of E.We can conclude that differences among genotypes in PIP1 expression affect Cl− exclusion from leaves, probably due to effects on water movement. Nevertheless, long-term salt treatments did not affect PIP expression in citrus plants, but reduced root hydraulic conductance and transpiration.