Plant Responses to Drought Stress and Exogenous ABA Application are Modulated Differently by Mycorrhization in Tomato and an ABA-deficient Mutant (Sitiens)

Abstract

The aims of the present study are to find out whether the effects of arbuscular mycorrhizal (AM) symbiosis on plant resistance to water deficit are mediated by the endogenous abscisic acid (ABA) content of the host plant and whether the exogenous ABA application modifies such effects. The ABA-deficient tomato mutant sitiens and its near-isogenic wild-type parental line were used. Plant development, physiology, and expression of plant genes expected to be modulated by AM symbiosis, drought, and ABA were studied. Results showed that only wild-type tomato plants responded positively to mycorrhizal inoculation, while AM symbiosis was not observed to have any effect on plant development in sitiens plants grown under well-watered conditions. The application of ABA to sitiens plants enhanced plant growth both under well-watered and drought stress conditions. In respect to sitiens plants subjected to drought stress, the addition of ABA had a cumulative effect in relation to that of inoculation with G. intraradices. Most of the genes analyzed in this study showed different regulation patterns in wild-type and sitiens plants, suggesting that their gene expression is modulated by the plant ABA phenotype. In the same way, the colonization of roots with the AM fungus G. intraradices differently regulated the expression of these genes in wild-type and in sitiens plants, which could explain the distinctive effect of the symbiosis on each plant ABA phenotype. This also suggests that the effects of the AM symbiosis on plant responses and resistance to water deficit are mediated by the plant ABA phenotype.

Insights On the Impact of Arbuscular Mycorrhizal Symbiosis On Tomato Tolerance to Water Stress

“…Previous work also studied the relationship between tomato and AM fungi under WS (Dell'Amico et al, 2002;Subramanian et al, 2006;Aroca et al, 2008;Wang et al, 2014;Ruiz-Lozano et al, 2016). The discrepancy among data already available could be due to the use of different plant varieties and fungal species/isolates as well as to different growth and drought stress conditions (Augé et al, 2015).…”

“…Although the role of AM fungi in plant WS tolerance has been well reported for several plant-AM fungus combinations, the underlying molecular mechanisms are still to be elucidated. The regulation of several genes putatively involved in the response to WS, such as aquaporin genes (Porcel et al, 2006), a gene (P5CS) encoding a rate-limiting enzyme of Pro synthesis (Porcel et al, 2004), and a gene (NCED) encoding a key enzyme in the abscisic acid (ABA) biosynthesis pathway (Aroca et al, 2008), has already been reported for AM-colonized plants under drought conditions. A potential water transport via AM fungus to the host plant has been suggested on the basis of the gene expression profiles for two functionally characterized fungal aquaporin genes, thus supporting the existence of a direct AM fungus involvement in plant tolerance to drought (Li et al, 2013a(Li et al, , 2013b.…”

Arbuscular mycorrhizal symbiosis enhanced growth and antioxidant metabolism in date palm subjected to long-term drought

“…Hydrogen peroxide content was determined according to Patterson's method (Patterson et al 1984) with slight modifications as described by Aroca et al (2008). Fivehundred milligrams of fresh leaves were homogenized in a cold mortar with 5 mL 5 % TCA containing 0.1 g of activated charcoal and 0.1 g PVPP.…”

Relative importance of an arbuscular mycorrhizal fungus (Rhizophagus intraradices) and root hairs in plant drought tolerance

“…AM fungi may also directly improve plant water relations by increasing root water absorption and leaf water potential, regulating transpiration rate (Augé 2001(Augé , 2004, and enhancing photosynthetic rates (Subramanian and Charest 1995). The underlying mechanisms for the aforementioned effects of mycorrhiza on water uptake may be the changes in plant drought-related gene expression, such as genes encoding aquaporins Porcel et al 2006;Li et al 2013) or genes encoding 9-cis-epoxycarotenoid dioxygenase (NCED), the key enzyme in the biosynthesis of abscisic acid (ABA) (Aroca et al 2008). The latter authors also reported that Rhizophagus intraradices significantly enhanced the expression of nced and other plant genes encoding plasma membrane intrinsic proteins (PIPs) in roots and resulted in a remarkable increase of shoot dry weight under drought conditions.…”