Manganese deficiency leads to genotype-specific changes in fluorescence induction kinetics and state transitions.

Barley (Hordeum vulgare) genotypes display a marked difference in their ability to tolerate growth at low manganese (Mn) concentrations, a phenomenon designated as differential Mn efficiency. Induction of Mn deficiency in two genotypes differing in Mn efficiency led to a decline in the quantum yield efficiency for both, although faster in the Mn-inefficient genotype. Leaf tissue and thylakoid Mn concentrations were reduced under Mn deficiency, but no difference between genotypes was observed and no visual Mn deficiency symptoms were developed. Analysis of the fluorescence induction kinetics revealed that in addition to the usual O-J-I-P steps, clear K and D steps were developed in the Mn-inefficient genotype under Mn deficiency. These marked changes indicated damages to photosystem II (PSII). This was further substantiated by state transition measurements, indicating that the ability of plants to redistribute excitation energy was reduced. The percentage change in state transitions for control plants with normal Mn supply of both genotypes was 9% to 11%. However, in Mn-deficient leaves of the Mn-inefficient genotypes, state transitions were reduced to less than 1%, whereas no change was observed for the Mn-efficient genotypes. Immunoblotting and the chlorophyll a/b ratio confirmed that Mn deficiency in general resulted in a significant reduction in abundance of PSII reaction centers relative to the peripheral antenna. In addition, PSII appeared to be significantly more affected by Mn limitation than PSI. However, the striking genotypic differences observed in Mn-deficient plants, when analyzing state transitions and fluorescence induction kinetics, could not be correlated with specific changes in photosystem proteins. Thus, there is no simple linkage between protein expression and the differential reduction in state transition and fluorescence induction kinetics observed for the genotypes under Mn deficiency.

Latent manganese deficiency increases transpiration in barley (Hordeum vulgare).

To investigate if latent manganese (Mn) deficiency leads to increased transpiration, barley plants were grown for 10 weeks in hydroponics with daily additions of Mn in the low nM range. The Mn-starved plants did not exhibit visual leaf symptoms of Mn deficiency, but Chl a fluorescence measurements revealed that the quantum yield efficiency of PSII (F(v)/F(m)) was reduced from 0.83 in Mn-sufficient control plants to below 0.5 in Mn-starved plants. Leaf Mn concentrations declined from 30 to 7 microg Mn g(-1) dry weight in control and Mn-starved plants, respectively. Mn-starved plants had up to four-fold higher transpiration than control plants. Stomatal closure and opening upon light/dark transitions took place at the same rate in both Mn treatments, but the nocturnal leaf conductance for water vapour was still twice as high in Mn-starved plants compared with the control. The observed increase in transpiration was substantiated by (13)C-isotope discrimination analysis and gravimetric measurement of the water consumption, showing significantly lower water use efficiency in Mn-starved plants. The extractable wax content of leaves of Mn-starved plants was approximately 40% lower than that in control plants, and it is concluded that the increased leaf conductance and higher transpirational water loss are correlated with a reduction in the epicuticular wax layer under Mn deficiency.

Differential capacity for high-affinity manganese uptake contributes to differences between barley genotypes in tolerance to low manganese availability.

There is considerable variability among barley (Hordeum vulgare) genotypes in their ability to grow in soils containing a low level of plant available manganese (Mn). The physiological basis for the tolerance to low Mn availability is unknown. In this work, Mn2+ influx and compartmentation in roots of the Mn-efficient genotype Vanessa and the Mn-inefficient genotype Antonia were investigated. Two separate Mn transport systems, mediating high-affinity Mn2+ influx at concentrations up to 130 nm and low-affinity Mn2+ influx at higher concentrations, were identified in both genotypes. The two genotypes differed only in high-affinity kinetics with the Mn-efficient genotype Vanessa having almost 4 times higher V(max) than the inefficient Antonia, but similar K(m) values. Online inductively coupled plasma-mass spectrometry measurements verified that the observed differences in high-affinity influx resulted in a higher Mn net uptake of Vanessa compared to Antonia. Further evidence for the importance of the differences in high-affinity uptake kinetics for Mn acquisition was obtained in a hydroponic system with mixed cultivation of the two genotypes at a continuously low Mn concentration (10-50 nm) similar to that occurring in soil solution. Under these conditions, Vanessa had a competitive advantage and contained 55% to 75% more Mn in the shoots than did Antonia. Subcellular compartmentation analysis of roots based on 54Mn2+ efflux established that up to 93% and 83% of all Mn was present in the vacuole in Vanessa and Antonia, respectively. It is concluded that differential capacity for high-affinity Mn influx contributes to differences between barley genotypes in Mn efficiency.