Influence of Polyethylene Glycol on Leaf Anatomy, Stomatal Behavior, Water Loss, and Some Physiological Traits of Date Palm Plantlets Grown In Vitro and Ex Vitro

Amal F M Zein El Din; Mohamed F M Ibrahim; Reham Farag; Hany G Abd El-Gawad; Ahmed El-Banhawy; Ibrahim A Alaraidh; Younes M Rashad; Islam Lashin; Ahmed Abou El-Yazied; Amr Elkelish; Ola H Abd Elbar

doi:10.3390/plants9111440

Influence of Polyethylene Glycol on Leaf Anatomy, Stomatal Behavior, Water Loss, and Some Physiological Traits of Date Palm Plantlets Grown In Vitro and Ex Vitro

Plants (Basel). 2020 Oct 26;9(11):1440. doi: 10.3390/plants9111440.

Affiliations

¹ The Central Laboratory for Date Palm Researches and Development, Agricultural Research Center, Giza 12619, Egypt.
² Department of Agricultural Botany, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.
³ Department of Horticulture, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.
⁴ Botany Department, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt.
⁵ Department of Botany and Microbiology, College of Science, King Saud University, Riyadh 2455, Saudi Arabia.
⁶ Plant Protection and Biomolecular Diagnosis Department, Arid Lands Cultivation Research Institute, City of Scientific Research and Technological Applications (SRTA-City), New Borg El-Arab City 21934, Egypt.
⁷ Botany and Microbiology Department, Faculty of Science, Al-Azhar University, Nasr City 11651, Cairo, Egypt.

Abstract

Few reports explain the mechanism of PEG action on stomatal behavior and anatomical structure and analyze the photosynthetic pigments of in vitro date palm plantlets for better tolerance to ex vitro exposure. The main challenge for in vitro micropropagation of date palm techniques remains restricted to high survival rates and vigorous growth after ex vitro transplantation. In vitro hardening is induced by Polyethylene glycol PEG (0.0, 10, 20, 30 g L^-1) for 4 weeks. Leaf anatomy, stomatal behavior, water loss %, photosynthetic pigments, and reducing sugars were examined in date palm plantlets (Phoenix dactylifera L.) cv. (Sewi) after 4 weeks from in vitro PEG treatment and after 4 weeks from ex vitro transplanting to the greenhouse. Leaf anatomy and the surface ultrastructure of in vitro untreated leaves showed a thin cuticle layer, wide opened malfunctioning stomata, and abnormal leaf anatomy. Furthermore, addition of PEG resulted in increasing cuticle thickness, epicuticular wax depositions, and plastids density, improving the stomatal ability to close and decreasing the stomatal aperture length while reducing the substomatal chambers and intercellular spaces in the mesophyll. As a result, a significant reduction in water loss % was observed in both in vitro and ex vitro PEG treated leaves as compared to untreated ones, which exhibited rapid wilting when exposed to low humidity for 4 h. PEG application significantly increased Chlorophylls a, b and carotenoids concentrations, especially 10, 20 g L^-1 treatments, which were sequentially reflected in increasing the reducing sugar concentration. However, leaves of plantlets treated with PEG at 30 g L^-1 became yellow and had necrosis ends with death. In vitro hardening by 20 g L^-1 PEG increased the survival rate of plantlets to 90% after ex vitro transfer compared to 63% recorded for the untreated plantlets. Therefore, this application provides normal date palm plantlets developed faster and enhances survival after ex vitro transfer.

Keywords: Phoenix dactylifera; ex vitro transfer; in vitro hardening; leaf anatomy; polyethylene glycol (PEG); stomata; survival; water loss %.

Grants and funding

RSP-2020/176/King Saud University