Involvement of aquaporins on nitrogen-acquisition strategies of juvenile and adult plants of an epiphytic tank-forming bromeliad

Interplay between nitric oxide and inorganic nitrogen sources in root development and abiotic stress responses

Nitrogen (N) is an essential nutrient for plants, and the sources from which it is obtained can differently affect their entire development as well as stress responses. Distinct inorganic N sources (nitrate and ammonium) can lead to fluctuations in the nitric oxide (NO) levels and thus interfere with nitric oxide (NO)-mediated responses. These could lead to changes in reactive oxygen species (ROS) homeostasis, hormone synthesis and signaling, and post-translational modifications of key proteins. As the consensus suggests that NO is primarily synthesized in the reductive pathways involving nitrate and nitrite reduction, it is expected that plants grown in a nitrate-enriched environment will produce more NO than those exposed to ammonium. Although the interplay between NO and different N sources in plants has been investigated, there are still many unanswered questions that require further elucidation. By building on previous knowledge regarding NO and N nutrition, this review expands the field by examining in more detail how NO responses are influenced by different N sources, focusing mainly on root development and abiotic stress responses.

Effects of low nitrogen supply on biochemical and physiological parameters related to nitrate and water, involving nitrate transporters and aquaporins in Citrus macrophylla

A reduction in chemical N-based fertillizer was investigated in Citrus plants. As N and water uptake are connected, the relationship between the physiological response to reductions in N was studied in relation to N metabolism and water. We examined the response of new and mature leaves and roots of Citrus macrophylla, grown under controlled conditions, and given different concentrations of N: 16, 8 or 4 mM. Differences in growth and development were determined for biochemical (mineral content, photosynthetic pigments, proteins and nitrate and nitrite reductase activity), physiological (photosynthesis and transpiration), and molecular (relative expression of nitrate transporters and aquaporins) parameters. Only plants given 4 mM N showed a reduction in growth. Although there were changes in NR activity, protein synthesis, and chlorophyll content in both 8 and 4 mM N plants that were highly related to aquaporin and nitrate transporter expression. The results revealed new findings on the relationship between aquaporins and nitrate transporters in new leaves of Citrus, suggesting a mechanism for ensuring growth under low N when new tissues are being formed.

Acid waters in tank bromeliads: Causes and potential consequences

PREMISE

The consequences of acidity for plant performance are profound, yet the prevalence and causes of low pH in bromeliad tank water are unknown despite its functional relevance to key members of many neotropical plant communities.

METHODS

We investigated tank water pH for eight bromeliad species in the field and for the widely occurring Guzmania monostachia in varying light. We compared pH changes over time between plant and artificial tanks containing a solution combined from several plants. Aquaporin transcripts were measured for field plants at two levels of pH. We investigated relationships between pH, leaf hydraulic conductance, and CO₂ concentration in greenhouse plants and tested proton pump activity using a stimulator and inhibitor.

RESULTS

Mean tank water pH for the eight species was 4.7 ± 0.06 and was lower for G. monostachia in higher light. The pH of the solution in artificial tanks, unlike in plants, did not decrease over time. Aquaporin transcription was higher for plants with lower pH, but leaf hydraulic conductance did not differ, suggesting that the pH did not influence water uptake. Tank pH and CO₂ concentration were inversely related. Fusicoccin enhanced a decrease in tank pH, whereas orthovanadate did not.

CONCLUSIONS

Guzmania monostachia acidified its tank water via leaf proton pumps, which appeared responsive to light. Low pH increased aquaporin transcripts but did not influence leaf hydraulic conductance, hence may be more relevant to nutrient uptake.

Molecular mechanisms of resistance to Myzus persicae conferred by the peach Rm2 gene: A multi-omics view

The transcriptomic and metabolomic responses of peach to Myzus persicae infestation were studied in Rubira, an accession carrying the major resistance gene Rm2 causing antixenosis, and GF305, a susceptible accession. Transcriptome and metabolome showed both a massive reconfiguration in Rubira 48 hours after infestation while GF305 displayed very limited changes. The Rubira immune system was massively stimulated, with simultaneous activation of genes encoding cell surface receptors involved in pattern-triggered immunity and cytoplasmic NLRs (nucleotide-binding domain, leucine-rich repeat containing proteins) involved in effector-triggered immunity. Hypersensitive reaction featured by necrotic lesions surrounding stylet punctures was supported by the induction of cell death stimulating NLRs/helpers couples, as well as the activation of H₂O₂-generating metabolic pathways: photorespiratory glyoxylate synthesis and activation of the futile P5C/proline cycle. The triggering of systemic acquired resistance was suggested by the activation of pipecolate pathway and accumulation of this defense hormone together with salicylate. Important reduction in carbon, nitrogen and sulphur metabolic pools and the repression of many genes related to cell division and growth, consistent with reduced apices elongation, suggested a decline in the nutritional value of apices. Finally, the accumulation of caffeic acid conjugates pointed toward their contribution as deterrent and/or toxic compounds in the mechanisms of resistance.

The function of high-affinity urea transporters in nitrogen-deficient conditions

Urea is the most used nitrogenous fertilizer worldwide and an important nitrogen-containing plant metabolite. Despite its major use as fertilizer, its direct uptake is limited due to the ubiquitous presence of bacterial urease, which leads to the formation of ammonium. In this review, we will focus mainly on the more recent research about the high-affinity urea transporter function in nitrogen-deficient conditions. The effective use of nitrogenous compounds is essential for plants to be able to deal with nitrogen-deficient conditions. Leaf senescence, either induced by development and/or by nitrogen deficiency, plays an important role in the efficient use of already assimilated nitrogen. Proteinaceous nitrogen is set free through catabolic reactions: the released amino acids from protein catabilization are in turn catabolized leading to an accumulation of ammonium and urea. The concentration and conversion to transportable forms of nitrogen, e.g. amino acids like glutamine and asparagine, are coordinated around the vascular tissue. Urea itself can be translocated directly over the phloem by a mechanism that involves DUR3, or it is converted by urease to ammonium and assimilated again into amino acids. The details of the high-affinity transporter function in this physiological context and the implications for crop yield are explained.