Drought Tolerance in Pinus halepensis Seed Sources As Identified by Distinctive Physiological and Molecular Markers

Abstract

Drought is one of the main constraints determining forest species growth, survival and productivity, and therefore one of the main limitations for reforestation or afforestation. The aim of this study is to characterize the drought response at the physiological and molecular level of different Pinus halepensis (common name Aleppo pine) seed sources, previously characterized in field trials as drought-sensitive or drought-tolerant. This approach aims to identify different traits capable of predicting the ability of formerly uncharacterized seedlings to cope with drought stress. Gas-exchange, water potential, photosynthetic pigments, soluble sugars, free amino acids, glutathione and proteomic analyses were carried out on control and drought-stressed seedlings in greenhouse conditions. Gas-exchange determinations were also assessed in field-planted seedlings in order to validate the greenhouse experimental conditions. Drought-tolerant seed sources presented higher values of photosynthetic rates, water use efficiency, photosynthetic pigments and soluble carbohydrates concentrations. We observed the same pattern of variation of photosynthesis rate and maximal efficiency of PSII in field. Interestingly drought-tolerant seed sources exhibited increased levels of glutathione, methionine and cysteine. The proteomic profile of drought tolerant seedlings identified two heat shock proteins and an enzyme related to methionine biosynthesis that were not present in drought sensitive seedlings, pointing to the synthesis of sulfur amino acids as a limiting factor for drought tolerance in Pinus halepensis. Our results established physiological and molecular traits useful as distinctive markers to predict drought tolerance in Pinus halepensis provenances that could be reliably used in reforestation programs in drought prone areas.

Effects of Drought and Salinity on European Larch (Larix decidua Mill.) Seedlings

“…Proline is one of the most typical compatible solutes in plants [68] and it has been reported to significantly increase in many plant species, including conifers, under different abiotic stress conditions. For example, drought or salinity treatments have been shown to cause Pro accumulation in pine species [69][70][71], or in spruce [27,49,72]. In one-month-old plantlets of Larix × eurolepis Henry (Larix decidua × Larix kaempferi) grown in the presence of cadmium, Pro contents were reported to increase about three-fold over control values [73], similarly to what we have detected in the present study in salt-treated European larch seedlings.…”

Roots of Lucerne Seedlings are More Resilient to a Water Deficit than Leaves or Stems

“…Taïbi [31] reported that free amino acids concentration could be used as a trait to identify the ability of Pinus halepensis in seedlings to cope with drought stress. The results of the present study showed that the concentration of proline in the roots, stems, and leaves increased under water stress with both moderate and severe water restrictions.…”

Responses to Drought in Seedlings of European Larch (Larix decidua Mill.) from Several Carpathian Provenances

“…They are diverse, however, and some like carotenoids and anthocyanins are known to play a role in photo-protection from oxidative stress resulting from various forms of abiotic stresses. There is a variation of photosynthetic pigments related to plants' phenology [52], but their reduction under water deficit conditions is common due to the reduction of chlorophyll synthesis, the inhibition of primary enzymes involved in photosynthesis, but also due to their degradation by chlorophyllase [53,54], and has been reported in several coniferous species under drought stress [41,[55][56][57][58]. The levels of photosynthetic pigments proved to be a reliable salt stress marker in European larch [40].…”

“…Besides its direct role in osmoregulation, Pro is involved in the protection of enzymes against denaturation and stabilization of protein synthesis, or may act as low-molecular weight chaperone, reactive oxygen species (ROS) scavenger or signaling molecule [59][60][61]. A strong increase in Pro under drought has been reported in many coniferous species, such as spruce [41,62], or pine [58,63], and fir [64]. In the genus Larix, a three-fold Pro increase has been reported in the hybrid L. x eurolepis when exposed to cadmium, or four-to seven-fold increase in L. decidua when exposed to salinity [65].…”