Short term salt treatment does not affect pistachio growth
Next, we examined the roots and shoots of salt treated plants for developmental changes. It is known that UCB1 plants show more robust growth, potentially as a result of hybrid vigor. Hence, in order to avoid size effects on salinity tolerance and sequestration, we used 8 weeks old UCB1 plants and 10 weeks old P. integerrima plants for all our assays. At these ages, the two genotypes have a virtually identical fresh weight (Fig. 2a, NS, two-way ANOVA) After one week of salt treatment, neither P. integerrima nor UCB1 showed significant decreases in root or shoot growth (Fig. 2a, NS, two-way ANOVA, Suppl. Fig 1a).
Since root system architecture remodeling is known to occur as a result of salinity stress (Koevoets et al., 2016), we assessed the root architecture and root weight of the treated plants. Although the root weight of UCB1 and P. integerrima were comparable (Fig. 2a), the UCB1 plants had more lateral roots compared to P. integerrima,and this difference was further enhanced after salt treatment (Fig. 2b, P<0.05 between genotypes, P<0.01 between treatment, two-way ANOVA, P=0.01 Tukey’s HSD). No significant difference in lateral root lengths between the two genotypes was observed (Supp. Fig. 1b, NS, two-way ANOVA). In Arabidopsis accession Columbia-0, low concentrations of salt have been shown to induce more lateral root initiation, possibly due to an enhanced cell cycle activity and cell elongation through increased Na+ vacuolar sequestration (Julkowska et al., 2014). Our results show that similar responses are occurring inPistacia spp. after short term salt treatment.