Contrasting Effects of GA 3 Treatments on Tomato Plants Exposed to - PDF document

J Plant Growth Regul (2010) 29:63–72 DOI 10.1007/s00344-009-9114-7 Contrasting Effects of GA 3 Treatments on Tomato Plants Exposed to Increasing Salinity Albino Maggio Æ Giancarlo Barbieri Æ Giampaolo Raimondi Æ Stefania De Pascale Received: 31 March 2009 / Accepted: 9 June 2009 / Published online: 6 August 2009 � Springer Science+Business Media, LLC 2009 Abstract The role of plant hormones under saline stress salinity nullified these differences. The fruit carotenoid is critical in modulating physiological responses that will level was generally lower in GA 3 -treated plants, indicating eventually lead to adaptation to an unfavorable environ- either an inhibitory effect of GA 3 treatment on carotenoid ment. Nevertheless, the functional level of plant hormones, biosynthesis or a reduced perception of the stress envi- and their relative tissue concentration, may have a different ronment by GA 3 -treated tomato plants. impact on plant growth and stress tolerance at increasing salinity of the root environment. Vigorous plant growth Abscisic acid � Carotenoids content � Keywords Cl - and Na ? accumulation � Leaf water potentials � may counteract the negative effects of salinization. In contrast, low gibberellin (GA) levels have been associated Stomatal regulation with reduced growth in response to salinity. Based on these facts and considering that the physiological basis of the cause-effect relationship between functional growth control Introduction and stress adaptation/survival is still a matter of debate, we hypothesized that exogenous applications of the plant Root zone salinization, a common phenomenon in irrigated hormone GA 3 may compensate for the salt-induced growth agriculture, may expose crop plants to ionic/osmotic stress deficiency and consequently facilitate tomato plant adap- and ultimately affect both final yield and quality (Flowers tation to a saline environment. GA 3 application (0 or 1999). The process of plant adaptation to salinity is mostly 100 mg GA 3 l - 1 ) was compared under four salinity levels, under hormonal control and involves the activation of obtained by adding equal increments of NaCl:CaCl 2 (2:1 stress response mechanisms, which mediate ionic/hydraulic molar basis) (EC = 2.5, 6.8, 11.7, 16.7 dS m - 1 ) to the re-equilibrium, reactive oxygen species (ROS) detoxifica- nutrient solution. GA 3 treatment reduced stomatal resis- tion, and modulation of cell growth/division (Hasegawa tance and enhanced plant water use at low salinity. These and others 2000; Zhu 2001; Ruggiero and others 2004; responses were associated with an increased number of Achard and others 2006). Although plant hormones have fruit per plant at harvest. However, moderate and high been proven to directly or indirectly control key aspects of plant growth and adaptation to adverse environments (Zhu 2002), the main features underlying the complex interac- tions between these metabolites are mostly unknown and only recently many important physiological cross-talks have begun to be unravelled (Nemhauser and others 2006). A. Maggio � G. Barbieri � G. Raimondi � S. De Pascale ( & ) The most characterized stress hormone is abscisic acid Department of Agricultural Engineering and Agronomy, (ABA), which is involved in pivotal physiological responses University of Naples Federico II, Via Universita `, 100, required for salt stress adaptation, including ion and water 80055 Portici, Naples, Italy homeostasis. ABA may directly control cell enlargement e-mail: depascal@unina.it and division (Ruggiero and others 2004), or indirectly A. Maggio modulate plant growth by increasing stomatal resistance, e-mail: albino.maggio@unina.it 123

64 J Plant Growth Regul (2010) 29:63–72 which restricts both water loss and CO 2 uptake. These Materials and Methods events are essential in overcoming temporary or long-term physiological perturbations and they contribute to both plant Growth Conditions adaptation and survival. In response to hyperosmotic stress, other hormones that primarily affect cell enlargement and The experiment was carried out at the Department of growth, such as gibberellins (GA), must also coordinately Agricultural Engineering and Agronomy of the University interact with ABA and possibly other stress metabolites, of Naples Federico II experimental greenhouse, Portici (Naples), Italy (40 � 49 0 N, 14 � 20 0 E). Seeds of cherry tomato including antioxidants and ROS scavengers (Achard and others 2006). It has been documented that ABA and GA play (Diamante F1—ESASEM 99-125) were germinated in sty- rofoam flats containing a mixture of sand and peat moss antagonistic roles in controlling many developmental pro- cesses, including germination, growth, and flowering (1:1) and subsequently transferred, at the stage of two fully (Razem and others 2006). On a biochemical basis, upstream expanded leaves (September 10), to 15-l buckets filled with regulation of the biosynthesis and balance between these perlite (Agrilit 3 Ø 2–5 mm) with one plant per bucket at the crop density of 3.5 plants m - 2 . The buckets were covered to two hormones may reside in the common precursor gera- nylgeranyl diphosphate (Hedden and Proebsting 1999; Ren avoid evaporative loss and equipped with two drippers with a nominal discharge of 2 l h - 1 . Plants were fertilized with and others 2007). Downstream checkpoints of their mode of action may involve the activation or inhibition of hydrolytic nutrient solution [electrical conductivity at 25 � C (EC) = 2.5 dS m - 1 ; pH = 6.0] containing (in mmol l - 1 ): 13.5 enzymes that have been proven to be critical for embryo 3 - , 8.75 K ? , 4.25 Ca 2 ? , 2.0 Mg 2 ? , - , 1.5 NH 4 ? , 1.25 PO 4 development (Rogers and Rogers 1992; Gubler and others NO 3 2 - , 3.0 Na ? , and 4.0 Cl - , plus micronutrients (B, 1995). Transcriptional regulation of ABA-mediated sup- 3.75 SO 4 0.03; Mn, 0.01; Fe, 0.015; Zn, 0.005; Cu, 0.00075; Mo, pression of GA responses has also been described (Xie and others 2006; Weiss and Ori 2007). Less clear are the 0.0005). The nutrient solutions were pumped from reservoir antagonistic functions of GA and ABA in terms of stomatal tanks (one 200-L tank per 15 plants) into the buckets. The regulation and their functional role in response to a hyper- surplus drained solution was then sent back to the tanks osmotic environment. based on a recirculating system. The number of pulses On a whole-plant basis and under field conditions, ranged from 3 to 6 per day (3-5 min/pulse). The reservoir compelling evidence indicates that vigorous plants may tanks were refilled with new nutrient solution every week. better cope with salinity (Munns and others 2006), possibly by delaying the onset of the salinity tolerance threshold Salt Stress Treatments (Dalton and others 2000). In contrast, both ABA- and GA- dependent growth reductions have been reported to be Two weeks after transplanting, the plants were divided into critical in stress adaptation and/or survival (Ruggiero and two groups of 180 single-plant buckets. One group was others 2004; Achard and others 2006; Magome and others irrigated with plain nutrient solution ( - GA 3 ), whereas the 2008). Although the independent roles of ABA and GA second group of plants ( ? GA 3 ) was irrigated with nutrient have been well documented (Zeevart and Creelman 1988; solution containing gibberellic acid (Gibrelex, 100 mg GA 3 l - 1 ) for 1 week (Levent Tuna and others 2008). Three Olszewski and others 2002), it remains uncertain how these two hormones coordinately regulate plant growth and stress weeks after transplanting, four salinity treatments were adaptation (Ross and O’Neill 2001). In this respect, there is imposed on both groups ( ? / - GA 3 ). To avoid NaCl-induced a clear need to unravel the physiological bases and genetic calcium deficiencies, equal increments of NaCl:CaCl 2 (2:1 determinants that control plant adaptation versus survival molar basis) were added to reach four different EC levels to link functional tolerance traits to specific agricultural (Maggio and others 2007): 2.5 (nonsalinized control = S0), 6.8 (S1), 11.7 (S2), 16.7 (S3) dS m - 1 , corresponding to 28 contexts (Maggio and others 2002). In a previous experi- ment we demonstrated that tomato plants respond to (S1), 55 (S2), 88 (S3) mM Na and 55 (S1), 111 (S2), 177 increasing salinity by activating metabolic/morphological (S3) mM Cl. The experimental design was a split-plot with adaptation mechanisms in a quite specific functional three replications. The GA 3 treatments were assigned to the sequence, which involves the control of plant growth and main plots and different salinity treatments were assigned to transition from vegetative to reproductive stages (Maggio the subplots, randomized within the main plots. Each and others 2007). In the present study we further analyzed salinity treatment consisted of 45 buckets (15 buckets per the functional role of GA and ABA in stress adaptation. replication). Photosynthetic photon flux density (PPFD), Here we demonstrate that exogenous GA applications may relative humidity (RH), and air temperature (T) were con- benefit plant growth and yield at low to moderate salinity, tinuously monitored during the experiment. EC and pH and whereas it may enhance stress sensitivity at moderate- to the amount of the nutrient solution collected weekly from high-salinity levels. each bucket also were measured and recorded. Plant water 123