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Title: Polyamines and other secondary metabolites of green-leaf and red-leaf almond rootstocks triggered in response to salinity

Author
item ZRIG, AHLEM - Faculty Of Sciences Of Gabes
item Ferreira, Jorge
item SERRANO, MARIA - Miguel Hernandez University
item VALERO, DANIEL - Miguel Hernandez University
item TOUNEKTI, TAIEB - Jazan University
item KHEMIRA, HABIB - Jazan University

Submitted to: Pakistan Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2018
Publication Date: 4/20/2018
Citation: Zrig, A., Ferreira, J.F., Serrano, M., Valero, D., Tounekti, T., Khemira, H. 2018. Polyamines and other secondary metabolites of green-leaf and red-leaf almond rootstocks triggered in response to salinity. Pakistan Journal of Botany. 50(4):1273-1279.

Interpretive Summary: Almond global production is over 1.5 million tons with the USA being the major producer, and with California being responsible for 100% of the crop yield. The US is followed by Spain, Syria, Italy, Iran and Morocco with minor production (2-3%) by Algeria, Tunisia, Greece, Turkey, Pakistan, and China. Although the crop requires plenty of fresh water, the production is reduced drastically when the water contains high levels of salts as almond trees are very sensitive to salinity. Salt-tolerant rootstocks may allow trees to achieve a reasonable yield with saline water. In this study, we added chloride salts of calcium and potassium to verify the extent to which chloride salts (alone or in combination with salinity) could alter accumulation of beneficial secondary metabolites in red or green leaf biotypes. One-month-old Bitter Almond (BA) and Garnem (GN15) rootstock seedlings were grown without salinity (control), or were exposed to irrigation with NaCl (75 mM) alone, or in combination with calcium chloride and/or potassium chloride. In green leaves of BA, the supplementation of saline solutions (with sodium chloride alone) with calcium increased anthocyanins (protective antioxidant leaf pigments) in both rootstocks, indicating that calcium chloride may increase the biosynthesis of the anthocyanins cyanidin and petunidin in red leaves of GN15. It seemed that the accumulation of cyanidin was involved in the osmotic regulation of the cell under salinity stress. The biosynthesis of the polyamines (organic compounds with two or more amino groups) spermidine and putrescine were also affected by salinity of irrigation waters. Spermidine increased significantly in GN15 plants when calcium chloride was added to control irrigation, but the highest increase in both spermidine and putrescine in GN15 was caused by sodium chloride alone. Results indicate that the significant increase in polyamines may be associated with the higher salt tolerance of GN15 and that the addition of calcium chloride may help plants cope with salinity stress by increasing the flavonoids cyanidin and petunidin in leaves of salinity-stressed almond rootstocks. Because selection of salinity-tolerant rootstocks may not depend solely on shoot and biomass accumulation under salinity, our results based on biochemical markers triggered by salinity may prove useful in helping researcher select almond trees for semiarid saline environments. They may also help almond farmers mitigate salinity stress by the addition of calcium chloride.

Technical Abstract: Almond trees are very sensitive to salinity, and saline water is the only alternative for irrigation in many semiarid regions. Thus, the use of salt-tolerant rootstocks may allow an economically-feasible yield under saline irrigation. In this study, we evaluated the effects of chloride salts on plant secondary metabolites in red-and green-leaf almond biotypes to improve salt tolerance. one-year-old rooted cuttings of Bitter Almond (BA) and Garnem (GN15) rootstock seedlings were cultivated for 3 weeks under low-salinity water (control), or exposed to irrigation with CaCl2 (10mM), KCl (10mM), and NaCl (75 mM), alone and in combination, for 4 weeks. In green leaves of BA, the supplementation of NaCl solutions with CaCl2 significantly increased anthocyanin, petunidin, and polyphenol concentration, indicating a possible involvement of these compounds in cell osmoregulation. In GN15 rootstock, spermidine increased significantly from control when CaCl2 was added to control irrigation. However, the highest and most significant increase in both spermidine and putrescine in GN15 was caused by NaCl alone. The significant increase in polyamines, between control to NaCl treatment, in GN15 but not in BA rootstock, and the drop in antioxidant capacity in BA, but not in GN15, across treatments, suggest that GN15 may be more salt-tolerant than BA. Although the addition of CaCl2 or KCl may not have any benefit in mitigating salinity in almond rootstocks, spermidine and putrescine may have a role in helping almond rootstocks cope with salinity.