© by PSP Volume 26 – No. 8/2017 pages 5103-5110 Fresenius Environmental Bulletin 5103 PHYSIOLOGICAL AND BIOCHEMICAL RESPONSES TO IRON STRESS CONDITIONS DEPEND ON GRAPEVINE GEN- OTYPE Gultekin Ozdemir 1,* , Semih Tangolar 2 , Hayriye Yildiz Dasgan 2 1 Dicle University, Faculty of Agriculture, Department of Horticulture, Diyarbakır, Turkey 2 Çukurova University, Faculty of Agriculture, Department of Horticulture, Adana, Turkey ABSTRACT One of the most common nutritional deficien- cies in vineyards is iron chlorosis due to high lime content and pH. In this study, physiological re- sponses to iron deficiency stress were compared in nine grapevine genotypes. For this purpose, plants were grown in hydroponic culture having low iron [(-) Fe] or sufficient iron/control [(+) Fe] conditions. The [(-) Fe] plants were grown with 10 -6 M Fe EDTA for 40 days followed by 2x10 -7 M FeEDTA for 20 days. [(+) Fe] plants were grown with 10 -4 M Fe EDTA. To create iron stress, 10 mM NaHCO3 was added to the solution. In plants, active and total iron contents (mg/L), shoot active and total iron contents (mg/L), leaf chlorophyll status (SPAD), and root fer- ric chelate reductase enzyme activity were exam- ined. All parameters were reduced in plants that were grown under iron deficient conditions. The highest active iron concentration in leaves was 108.27 mg/L in 1103 P grown in [(+) Fe] conditions. The chloro- phyll content of leaves was 27.93 (1616 C) in [(+) Fe] conditions. The ferric chelate reductase enzyme activity of roots was higher in iron stress conditions. The highest level was 1395.78 in the 140 Ru geno- type. KEYWORDS: Grapevine, Iron Stress, Chlorosis, Tolerance, Ferric che- late reductase INTRODUCTION Many horticultural crops grown in calcareous soils suffer from iron deficiency stress [34]. Iron de- ficiency is generally characterized by inter-vein yel- lowing in young leaves. Different stress responses are seen under iron deficient conditions depending on the affected region of the plant (shoot, leaf or root), plant age, plant growth area, and plant culti- vars. The plant species mainly affected include grapes [1, 2, 3, 32]. It has been known for 160 years that iron is es- sential for plant growth [4, 5]. Previous studies on iron uptake in plants address iron accessibility in roots [6], iron deficiency in calcareous soils [2, 3], plant sensitivity to iron chlorosis [4, 7], iron adapta- tion mechanisms [7, 8, 9], and prevention of iron chlorosis [1, 10]. Iron chlorosis is an important nutritional defi- ciency in vineyards [17, 18]. Grapevine cultivars that can use iron in alkaline soils are called Fe-efficient, while cultivars that develop iron chlorosis are called Fe-inefficient [35]. Independent of the iron nutri- tional status of the plant, mobilization of iron in the soil is due to different uptake mechanisms. These up- take mechanisms are activated in Fe-efficient plants in response to iron stress. Iron deficiency symptoms (leaf chlorosis and depressed growth) are common in grapevines grow- ing on calcareous soils [12]. Certain grapevine genotypes are particularly susceptible to iron deficiency stress when grown on calcareous soils [33]. Vitis species differ in their de- gree of susceptibility to high pH and calcareous soils [13, 14, 15]. Vitis vinifera L. is calcareous-tolerant, but other varieties vary in their ability to tolerate cal- careous soils [2, 3]. Varieties are frequently sub- jected to iron deficiency when grown in calcareous soils that contain high concentrations of bicarbonate [16, 43]. Mechanisms by which grapevines adapt to low iron conditions differ among genotypes and can be classified according to two strategies [6, 9, 19]. Upon experiencing low iron availability in soils, grapevines (Vitis sp.) respond as typical Strat- egy I plants. Various grapevine rootstocks show quantitative differences in root response reactions in- volved in Strategy I [49]. The adaptive response in- volves morphological and physiological changes in the grapevine roots [20, 21, 22]. Strategy I is exhib- ited by most higher plants, including dicotyledons and monocotyledons (except for grasses), and it con- sists of four types of responses in the roots [6,7,10]. These responses include 1) enhanced H - ion release, 2) formation of rhizodermal or hypodermal transfer cells, 3) enhanced ferric iron reduction to ferrous iron, and 4) enhanced release of chelating com- pounds such as phenolics [37,38]. Iron deficiency stress represents a physiologi- cal phenomenon with negative impact on the quality and quantity of grape production in vineyards [11].