Low auxin sensitivity of diageotropica tomato mutant alters nitrogen deficiency response.

Plant responses to nitrogen supply are dependent on auxin signaling, but much still remains to be elucidated regarding N deficiency in tomato. Thus, the objective of this work was to evaluate how low auxin sensitivity regulates the responses of tomato plants to N deficiency. For this purpose, we used the tomato diageotropica mutant, with low auxin sensitivity, and a near isogenic line cv. Micro-Tom grown in nutrient solutions under absence and presence of nitrogen. Plant height, stem diameter, root and shoot dry mass, area and root density, number of lateral roots, leaf area, chlorophylls and carotenoids content, nitrogen accumulation and nitrogen use efficiency were evaluated. We observed a clear interaction between the tomato genotype and nitrogen. When the plants were grown with nitrogen, 'Micro-Tom' showed higher growth than the diageotropica mutant. Under nitrogen deficiency condition, the mutant showed improved growth, nitrogen use efficiency and higher contents of pigments. In general, the low sensitivity to auxin in diageotropica caused reduced growth in both shoot and root. However, the diageotropica tomato showed a positive regulation of the nitrogen use efficiency under nitrogen deficiency. In general, our data revealed that the reduced sensitivity to auxin increased the adaptive capacity to the nitrogen deficiency.

Effects of hormonal priming on seed germination of pigeon pea under cadmium stress.

In this work we investigated whether priming with auxin, cytokinin, gibberellin, abscisic acid and ethylene, alters the physiological responses of seeds of pigeon pea germinated under water and cadmium stress. Seeds treated with water or non-treated seeds were used as control. Although compared to non-treated seeds we found that the hormone treatments improve the germination of pigeon pea under cadmium stress, however, these treatments did not differ from water. However, we also observed a trend of tolerance to the effects of cadmium in the presence of ethylene, suggesting that the use of this hormone may be an efficient method to overcome seed germination under metal stress.

Biochemical and histological characterization of tomato mutants.

Biochemical responses inherent to antioxidant systems as well morphological and anatomical properties of photomorphogenic, hormonal and developmental tomato mutants were investigated. Compared to the non-mutant Micro-Tom (MT), we observed that the malondialdehyde (MDA) content was enhanced in the diageotropica (dgt) and lutescent (l) mutants, whilst the highest levels of hydrogen peroxide (H(2)O(2)) were observed in high pigment 1 (hp1) and aurea (au) mutants. The analyses of antioxidant enzymes revealed that all mutants exhibited reduced catalase (CAT) activity when compared to MT. Guaiacol peroxidase (GPOX) was enhanced in both sitiens (sit) and notabilis (not) mutants, whereas in not mutant there was an increase in ascorbate peroxidase (APX). Based on PAGE analysis, the activities of glutathione reductase (GR) isoforms III, IV, V and VI were increased in l leaves, while the activity of superoxide dismutase (SOD) isoform III was reduced in leaves of sit, epi, Never ripe (Nr) and green flesh (gf) mutants. Microscopic analyses revealed that hp1 and au showed an increase in leaf intercellular spaces, whereas sit exhibited a decrease. The au and hp1 mutants also exhibited a decreased in the number of leaf trichomes. The characterization of these mutants is essential for their future use in plant development and ecophysiology studies, such as abiotic and biotic stresses on the oxidative metabolism.

Cryptochrome 1a of tomato mediates long-distance signaling of soil water deficit.

Although the blue light photoreceptors cryptochromes mediate the expression of genes related to reactive oxygen species, whether cryptochrome 1a (cry1a) regulates local and long-distance signaling of water deficit in tomato (Solanum lycopersicum L.) is unknown. Thus the cry1a tomato mutant and its wild-type (WT) were reciprocally grafted (WT/WT; cry1a/cry1a; WT/cry1a; cry1a/WT; as scion/rootstock) or grown on their own roots (WT and cry1a) under irrigated and water deficit conditions. Plant growth, pigmentation, oxidative stress, water relations, stomatal characteristics and leaf gas exchange were measured. WT and cry1a plants grew similarly under irrigated conditions, whereas cry1a plants had less root biomass and length and higher tissue malondialdehyde concentrations under water deficit. Despite greater oxidative stress, cry1a maintained chlorophyll and carotenoid concentrations in drying soil. Lower stomatal density of cry1a likely increased its leaf relative water content (RWC). In grafted plants, scion genotype largely determined shoot and root biomass accumulation irrespective of water deficit. In chimeric plants grown in drying soil, cry1a rootstocks increased RWC while WT rootstocks maintained photosynthesis of cry1a scions. Manipulating tomato CRY1a may enhance plant drought tolerance by altering leaf pigmentation and gas exchange during soil drying via local and long-distance effects.

Abscisic acid-deficient sit tomato mutant responses to cadmium-induced stress.

There is a very effective cross-talk between signals triggered by reactive oxygen species and hormonal responses in plants, activating proteins/enzymes likely to be involved in stress tolerance. Abscisic acid (ABA) is known as a stress hormone that takes part in the integration of signals. This work aimed to characterize the biochemical response and ultrastructural changes induced by cadmium (Cd) in the Micro-Tom (MT) sitiens ABA-deficient mutant (sit) and its wild-type (MT) counterpart. MT and sit plants were grown over a 96-h period in the presence of Cd (0, 10, and 100 µM CdCl2). The overall results indicated increases in lipid peroxidation, hydrogen peroxide content and in the activities of the key antioxidant enzymes such as catalase, glutathione reductase, and ascorbate peroxidase in both genotypes. On the other hand, no alteration was observed in chlorophyll content, while the activity of another antioxidant enzyme, superoxide dismutase, remained constant or even decreased in the presence of Cd. Roots and shoots of the sit mutant and MT were analyzed by light and transmission electron microscopy in order to characterize the structural changes caused by the exposure to this metal. Cd caused a decrease in intercellular spaces in shoots and a decrease in cell size in roots of both genotypes. In leaves, Cd affected organelle shape and internal organization of the thylakoid membranes, whereas noticeable increase in the number of mitochondria and vacuoles in MT and sit roots were observed. These results add new information that should help unravel the relative importance of ABA in regulating the cell responses to stressful conditions induced by Cd apart from providing the first characterization of this mutant to oxidative stress.

Biochemical dissection of diageotropica and Never ripe tomato mutants to Cd-stressful conditions.

In order to further address the modulation of signaling pathways of stress responses and their relation to hormones, we used the ethylene-insensitive Never ripe (Nr) and the auxin-insensitive diageotropica (dgt) tomato mutants. The two mutants and the control Micro-Tom (MT) cultivar were grown over a 40-day period in the presence of Cd (0.2 mM CdCl2 and 1 mM CdCl2). Lipid peroxidation, leaf chlorophyll, proline content, Cd content and antioxidant enzyme activities in roots, leaves and fruits were determined. The overall results indicated that the MT genotype had the most pronounced Cd damage effects while Nr and dgt genotypes might withstand or avoid stress imposed by Cd. This fact may be attributed, at least in part, to the fact that the known auxin-stimulated ethylene production is comprised in dgt plants. Conversely, the Nr genotype was more affected by the Cd imposed stress than dgt, which may be explained by the fact that Nr retains a partial sensitivity to ethylene. These results add further information that should help unraveling the relative importance of ethylene in regulating the cell responses to stressful conditions.

Convergence of developmental mutants into a single tomato model system: 'Micro-Tom' as an effective toolkit for plant development research.

BACKGROUND: The tomato (Solanum lycopersicum L.) plant is both an economically important food crop and an ideal dicot model to investigate various physiological phenomena not possible in Arabidopsis thaliana. Due to the great diversity of tomato cultivars used by the research community, it is often difficult to reliably compare phenotypes. The lack of tomato developmental mutants in a single genetic background prevents the stacking of mutations to facilitate analysis of double and multiple mutants, often required for elucidating developmental pathways. RESULTS: We took advantage of the small size and rapid life cycle of the tomato cultivar Micro-Tom (MT) to create near-isogenic lines (NILs) by introgressing a suite of hormonal and photomorphogenetic mutations (altered sensitivity or endogenous levels of auxin, ethylene, abscisic acid, gibberellin, brassinosteroid, and light response) into this genetic background. To demonstrate the usefulness of this collection, we compared developmental traits between the produced NILs. All expected mutant phenotypes were expressed in the NILs. We also created NILs harboring the wild type alleles for dwarf, self-pruning and uniform fruit, which are mutations characteristic of MT. This amplified both the applications of the mutant collection presented here and of MT as a genetic model system. CONCLUSIONS: The community resource presented here is a useful toolkit for plant research, particularly for future studies in plant development, which will require the simultaneous observation of the effect of various hormones, signaling pathways and crosstalk.