Abstract 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.

ABSTRACT Ammonium (NH4 +) toxicity in yellow passionfruit (Passiflora edulis Sims f. flavicarpa O. Deg.) may be mitigated by Si application. This study aimed to evaluate the interaction effect of Si and high level of NH4 + on yellow passionfruit seedlings nutrition, physiology, growth, and DM production. Pots were filled with pinus bark and nutrition solution was applied. Treatments were arranged in a completely randomized design, with five replicates, in a 2 × 2 factorial scheme: two ratios of NH4 + and nitrate, NO3 + (40/60%, without high level of NH4 +; and 75/25%, with high level of NH4 +) at N concentration of 13 mmol N L-1, in the absence and presence of Si (2.0 mmol L-1). Sixty days after seedling transplant it was evaluated: N, Si, K, Ca and Mg root and shoots accumulation, leaf green color index (GCI), electrolyte leakage index (ELI), intracellular CO2 concentration (Ci), transpiration rate (Tr), stomatal conductance (gs), net photosynthesis rate (Pn), stem diameter, leaf area, root length, N use efficiency (NUE) and root and shoot DM content. Plants cultivated with Si had 19.1% and 16.3% lower Tr and gs, respectively, regardless NH4 + concentration. Moreover, Ci and Pn were 13.2% and 16.4%, respectively, higher in plants that received Si. Plants cultivated under high NH4 + concentrations, with Si application had 17% bigger stem diameter and 15.4% bigger root length than plants without Si application. Si application in yellow passionfruit seedlings cultivated with high level of NH4 + increased accumulation and NUE, root length, root DM, and GCI. In addition, Si application reduced ELI, which resulted in higher stem diameter. These results prove that Si application mitigates NH4 + toxicity in yellow passionfruit seedlings

Abstract Phalaenopsis and Dendrobium do not grow and flower well with 100% ammonium (NH4-N); and there are detailed studies on the effects of nitrate (NO3-N) and ammonium ratios on the flowering, but no information about accumulation of other nutrients and the effects of ammonium toxicity on orchids. For this reason, two experiments were carried out with orchids: Phalaenopsis ‘Golden Peoker’ and Dendrobium ‘Valentine’. Six months after acclimatization the plants were transplanted to individual plastic vessels and the treatments consisted of five ratios (%) of nitrate / ammonium (0/100, 25/75, 50/50, 75/25, 100/0). The sources of NO3-N and NH4-N were calcium nitrate and ammonium sulfate, respectively. After 12 months treatment, when the plants were beginning to issuance of flower stem, the accumulation of: N, P, K, Ca and Mg in the shoot and biometric variables were evaluated for both species. The NH4-N ratio of 40% and 50% of the total nitrogen benefited the growth of Phalaenopsis and Dendrobium, respectively. The application of higher proportions of ammonium resulted in decreased N, K, Ca and Mg absorption, index of green color and increased leakage of electrolytes in Phalaenopsis and Dendrobium. NH4-N proportions greater than 75% for 12 months caused toxicity in Phalaenopsis and Dendrobium.