Mechanical stimulation of trigger hairs on the adaxial surface of the trap of Dionaea muscipula leads to the generation of action potentials and to rapid leaf movement. After rapid closure secures the prey, the struggle against the trigger hairs results in generation of further action potentials which inhibit photosynthesis. A detailed analysis of chlorophyll a fluorescence kinetics and gas exchange measurements in response to generation of action potentials in irritated D. muscipula traps was used to determine the ‘site effect’ of the electrical signal-induced inhibition of photosynthesis. Irritation of trigger hairs and subsequent generation of action potentials resulted in a decrease in the effective photochemical quantum yield of photosystem II (ΦPSII) and the rate of net photosynthesis (AN). During the first seconds of irritation, increased excitation pressure in photosystem II (PSII) was the major contributor to the decreased ΦPSII. Within ∼1 min, non-photochemical quenching (NPQ) released the excitation pressure at PSII. Measurements of the fast chlorophyll a fluorescence transient (O-J-I-P) revealed a direct impact of action potentials on the charge separation–recombination reactions in PSII, although the effect seems to be small rather than substantial. All the data presented here indicate that the main primary target of the electrical signal-induced inhibition of photosynthesis is the dark reaction, whereas the inhibition of electron transport is only a consequence of reduced carboxylation efficiency. In addition, the study also provides valuable data confirming the hypothesis that chlorophyll a fluorescence is under electrochemical control.

While the importance of cell type specificity in plant adaptive responses is widely accepted, only a limited number of studies have addressed this issue at the functional level. We have combined electrophysiological, imaging, and biochemical techniques to reveal the physiological mechanisms conferring higher sensitivity of apical root cells to salinity in barley (Hordeum vulgare). We show that salinity application to the root apex arrests root growth in a highly tissue-and treatment-specific manner. Although salinity-induced transient net Na + uptake was about 4-fold higher in the root apex compared with the mature zone, mature root cells accumulated more cytosolic and vacuolar Na + , suggesting that the higher sensitivity of apical cells to salt is not related to either enhanced Na + exclusion or sequestration inside the root. Rather, the above differential sensitivity between the two zones originates from a 10-fold difference in K + efflux between the mature zone and the apical region (much poorer in the root apex) of the root. Major factors contributing to this poor K + retention ability are (1) an intrinsically lower H + -ATPase activity in the root apex, (2) greater saltinduced membrane depolarization, and (3) a higher reactive oxygen species production under NaCl and a larger density of reactive oxygen species-activated cation currents in the apex. Salinity treatment increased (2-to 5-fold) the content of 10 (out of 25 detected) amino acids in the root apex but not in the mature zone and changed the organic acid and sugar contents. The causal link between the observed changes in the root metabolic profile and the regulation of transporter activity is discussed.

No abstract

Salinity stress tolerance is a physiologically complex trait that is conferred by the large array of interacting mechanisms. Among these, vacuolar Na+ sequestration has always been considered as one of the key components differentiating between sensitive and tolerant species and genotypes. However, vacuolar Na+ sequestration has been rarely considered in the context of the tissue-specific expression and regulation of appropriate transporters contributing to Na+ removal from the cytosol. In this work, six bread wheat varieties contrasting in their salinity tolerance (three tolerant and three sensitive) were used to understand the essentiality of vacuolar Na+ sequestration between functionally different root tissues, and link it with the overall salinity stress tolerance in this species. Roots of 4-day old wheat seedlings were treated with 100 mM NaCl for 3 days, and then Na+ distribution between cytosol and vacuole was quantified by CoroNa Green fluorescent dye imaging. Our major observations were as follows: (1) salinity stress tolerance correlated positively with vacuolar Na+ sequestration ability in the mature root zone but not in the root apex; (2) contrary to expectations, cytosolic Na+ levels in root meristem were significantly higher in salt tolerant than sensitive group, while vacuolar Na+ levels showed an opposite trend. These results are interpreted as meristem cells playing a role of the “salt sensor;” (3) no significant difference in the vacuolar Na+ sequestration ability was found between sensitive and tolerant groups in either transition or elongation zones; (4) the overall Na+ accumulation was highest in the elongation zone, suggesting its role in osmotic adjustment and turgor maintenance required to drive root expansion growth. Overall, the reported results suggest high tissue-specificity of Na+ uptake, signaling, and sequestration in wheat roots. The implications of these findings for plant breeding for salinity stress tolerance are discussed.

No abstract

Stronger Na+ extrusion and vacuolar sequestration are essential to confer better salt tolerance in bread wheat than in durum wheat. Removal of the root meristems increased salt sensitivity in wheat.

Polyamine (PA) levels in plants increase considerably under saline conditions. Because such an increase is believed to be beneficial for stress resistance, exogenous application of PAs has often been advocated as a means of ameliorating the detrimental effects of salinity. Results, however, are rather controversial, ranging from a significant amelioration to being ineffective or even toxic. The reasons for this controversy remain elusive. The ability of a root to retain K(+) in the presence of NaCl was used as a physiological indicator to evaluate the ameliorative effects of PA. Pre-treatment with 1 mM Spm(4+) (spermine), Spd(3+) (spermidine) or Put(2+) (putrescine) prevented salt-induced K(+) leak only in the mature root zone of hydroponically grown maize and Arabidopsis. In contrast, in the distal elongation root zone, PA pre-treatment resulted in an even larger NaCl-induced K(+) efflux, with the effect ranging from Spm(4+) >Spd(3+ )= Put(2+). A similar sequence has been also reported for H(+) pump inhibition, measured for both root zones. It appears that PAs affect cell membrane transporters in a highly specific way, with a relatively narrow 'window' in which amelioration is observed. We suggest that the ameliorative affect of PAs is the result of a complex combination of factors which might potentially include PA transport and accumulation in the cell cytosol, their metabolization and the functional expression of the specific target proteins or signaling elements.

Many plant-derived chemicals may have an impact on the functioning of the animal brain. The mechanisms by which the psychoactive components of these various products have their effects have been widely described, but the question of why they have these effects has been almost totally ignored. Recent evidence suggests that plants may produce chemicals to manipulate their partner ants and to make reciprocation more beneficial. In the present review we propose that these plant-derived chemicals could have evolved in plants to attract and manipulate ant behaviour; this would place the plant–animal interaction in a different ecological context and open new ecological and neurobiological perspectives for drug seeking and use.