pubs.acs.org/JAFC Published on Web 05/28/2010 © 2010 American Chemical Society 7226 J. Agric. Food Chem. 2010, 58, 7226–7232 DOI:10.1021/jf101221t Exogenous Gibberellic Acid Reprograms Soybean to Higher Growth and Salt Stress Tolerance MUHAMMAD HAMAYUN, † SUMERA AFZAL KHAN, ‡ ABDUL LATIF KHAN, †,§ JAE-HO SHIN, † BASHIR AHMAD, ‡ DONG-HYUN SHIN, † AND IN-JUNG LEE* ,† † School of Applied Biosciences, College of Agriculture and Life Sciences, Kyungpook National University, South Korea, ‡ Centre of Biotechnology and Microbiology, University of Peshawar, Pakistan, and § Kohat University of Science and Technology, Pakistan The agricultural industry is severely affected by salinity due to its high magnitude of adverse impacts and worldwide distribution. We observed the role of exogenous gibberellic acid (GA 3 ) in salinity alleviation of soybean. We found that GA 3 application significantly promoted plant length and plant fresh/dry biomass while markedly hindered by NaCl induced salt stress. The adverse effect of salt stress was mitigated by GA 3 , as growth attributes significantly recovered, when GA 3 was added to salt stressed soybean plants. Elevated GA 3 treatments increased daidzein and genistein contents (commonly known as phytoestrogens) of soybean leaves under control and salt stress conditions. Phytohormonal analysis of soybean showed that the level of bioactive gibberellins (GA 1 and GA 4 ) and jasmonic acid increased in GA 3 treated plants, while the endogenous abscisic acid and salicylic acid contents declined under the same treatment. GA 3 mitigated the adverse effects of salt stress by regulating the level of phytohormones, thus aiding the plant in resuming its normal growth and development. The presence of GA 1 and GA 4 showed that both early-C13-hydroxylation and non- C13-hydroxylation pathways of GA biosynthesis are functional in soybean. It was concluded that GA 3 ameliorates the adverse effects of salt stress and restores normal growth and development of soybean. KEYWORDS: Soybean; gibberellic acid; salinity stress; jasmonic acid; salicylic acid; abscisic acid INTRODUCTION The human population continues to grow, whereas the size of arable land is on decline as it is rendered unfavorable for cultivation due to various environmental constraints, and greater emphasis must be given to bringing marginally productive and nonarable land under production. Salinity of soil and water is a major problem that restricts yield on almost 40 million hectares of irrigated land, which is approximately one-third of the irrigated land on earth ( 1 ). It was estimated that about 50% of the arable land will be affected by salt stress by the year 2050 ( 2 ). Saline soils possess high levels of sodium (Na þ ) and chloride (Cl - ) contents and thus exert adverse abiotic stress on plants. Scientists are working on the reclamation of saline lands, and much attention is now focused on the use of plant growth regulators, which are known to be involved in the regulation of plant responses to the external environment and to control a number of stress-induced genes ( 3 ). Salt stress disturbs normal growth and development of plants by altering physiological and biochemical processes. The re- sponse of plants to salt stress depends on multiple factors, but phytohormones are thought to be the most important endoge- nous substances involved in the mechanisms of tolerance or susceptibility of plants ( 4 ). Many of the proteins produced by the plant under abiotic stress are induced by phytohormones, such as abscisic acid ( 5 ), salicylic acid ( 6 ), and jasmonates ( 7 ). These plant growth hormones are usually present in minute quantities but play a pivotal role in growth and development processes. For instance, gibberellins (GAs) affect stem elonga- tion, flowering, fruit development, and seed germination ( 8 ), while abscisic acid (ABA) being a generic stress hormone is upregulated by salinity and induces genes involved in salt and osmotic alleviation ( 9 ). Jasmonic acid (JA) influences seed germination, root growth, fertility, fruit ripening, and senes- cence ( 10 , 11 ), and activates plant defense mechanisms in re- sponse to insect-driven wounding, pathogens, and environmental stresses including drought, low temperature, and salinity ( 12 ). Salicylic acid (SA) is an important signal substance that induces systemic acquired resistance (SAR) against pathogen attack on plants ( 13 ). Soybean is an important source of nutrition in the world and is popularly known as a healthy food in many Asian countries. Soybean crop is grown for oil production, and a smaller percent- age of soybeans are used directly for human consumption. In China, Japan, and Korea, soybean and products made from the bean (miso, natto, tofu, douchi, doenjang, chungkookjang, ganjang, and others) are part of the daily diet. In Korean cuisine, soybean sprouts (kongnamul) are used in a variety of dishes. *To whom correspondence should be addressed. Phone: þ82-53- 950-5708. Fax: þ82-53-958-6880. E-mail: ijlee@knu.ac.kr.