Tree Physiology - Advance Access

Morphology and oxidative physiology of boron-deficient mulberry plants

Tewari, R. K., Kumar, P., Sharma, P. N. — Fri, 20 Nov 2009 17:31:16 PST

The aim of the study was to induce B deficiency symptoms and to relate the generation of reactive oxygen species (ROS) and altered cellular redox environment with the effects of B deficiency in mulberry (Morus alba L.) cv. Kanva-2 plants. Study was undertaken on antioxidant responses, malondialdehyde (MDA) content as an indicator of oxidative damage and ratio of dehydroascorbate (DHA) to ascorbic acid (AsA) as an index of cellular redox environment in B-deficient (0.0 µM) and B-supraoptimal (33 µM) mulberry plants. B deficiency symptoms appeared as upward cupping of the young emerging leaves. Later on, B-deficient plants developed lenticels like cracks on major vein, petiole and stem. B-deficient leaves had higher water potential () and relative water content (RWC), contained a lower concentration of B, less chloroplastic pigments and high tissue Fe, Mn and Zn concentrations compared to the controls. Hydrogen peroxide was accumulated in leaves of B-deficient and B-supraoptimal plants. B-supraoptimal plants also showed an increased DHA/AsA ratio. The activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7) and ascorbate peroxidase (APX, EC 1.11.1.11) were increased in B-deficient leaves. The activities of SOD and POD were decreased in B-supraoptimal plants. The results suggest that B deficiency aggravates oxidative stress through enhanced generation of ROS in mulberry plants.

Leaf gas exchange, chlorophyll fluorescence and pigment indexes of Eugenia uniflora L. in response to changes in light intensity and soil flooding

Mielke, M. S., Schaffer, B. — Wed, 18 Nov 2009 06:25:49 PST

The interactive effects of changing light intensity and soil flooding on the photosynthetic performance of Eugenia uniflora L. (Myrtaceae) seedlings in containers were examined. Two hypotheses were tested: (i) the photosynthetic apparatus of shade-adapted leaves can be rapidly acclimated to high light after transfer from shade to full sun, and (ii) photosynthetic acclimation to changing light intensity may be influenced by soil flooding. Seedlings cultivated in a shade house (40% of full sun, 12 mol m^–² day^–¹) for 6 months were transferred to full sun (20–40 mol m^–2 day^–1) or shade (30% of full sun, 8 mol m^–2 day^–1) and subjected to soil flooding for 23 days or not flooded. Chlorophyll content index (CCI), chlorophyll fluorescence, leaf weight per area (LWA), photosynthetic light–response curves and leaf reflectance indexes were measured during soil flooding and after plants were unflooded. The CCI values increased throughout the experiment in leaves of shaded plants and decreased in leaves of plants transferred to full sun. There were no significant interactions between light intensity and flooding treatments for most of the variables analyzed, with the exception of Fv/Fm 22 days after plants were flooded and 5 days after flooded plants were unflooded. The light environment significantly affected LWA, and light environment and soil flooding significantly affected the light-saturated gross CO₂ assimilation rate expressed on area and dry weight bases (A_max-area and A_max-wt, respectively), stomatal conductance of water vapor (g_ssat) and intrinsic water use efficiency (A/g_s). Five days after flooded plants were unflooded, the normalized difference vegetation index (NDVI) and the scaled photochemical reflectance index (sPRI) were significantly higher in shade than in sun leaves. Thirty days after transferring plants from the shade house to the light treatment, LWA was 30% higher in sun than in shade leaves, and A_max_-area and g_ssat were 59% and 99% higher, respectively, in shade than in sun leaves. Changes in CCI, NDVI and sPRI in leaves of E. uniflora seedlings transferred from shade to full sun appear to be associated with changes in pigment composition and protective mechanisms against excess light.

Changes in antioxidant enzyme activities and isozyme profiles in leaves of male and female Populus cathayana infected with Melampsora larici-populina

Zhang, S., Lu, S., Xu, X., Korpelainen, H., Li, C. — Mon, 16 Nov 2009 07:14:42 PST

Populus cathayana Rehd., a dioecious tree species, is widely distributed in the northern, central and southwestern regions of China. In poplars, Melampsora larici-populina Kleb. is mainly responsible for rust disease, which is considered to be the world's most important disease of poplars. Yet, little is known about sex-related responses to rust disease in poplars. The purpose of this work was to determine whether sexually different responses occur in the antioxidant system of poplars after infection by rust disease. Three-month-old male and female P. cathayana individuals were inoculated with M. larici-populina in a greenhouse. After 12 days of incubation, we investigated the changes in physiology, biochemistry, enzyme activities and isozyme profiles. It was discovered that (i) leaf rust disease inhibited photosynthesis, caused oxidative stress and cellular membrane damage and changed antioxidant enzyme activities and isozyme profiles in poplar leaves; (ii) male poplars suffered from lower infection levels and less negative effects of leaf rust disease than did females; (iii) males showed higher antioxidant activities and less H₂O₂ accumulation than did females after being infected by leaf rust. Thus, our results indicate that leaf rust disease is more severe in female poplars, and they suffer from greater negative effects than do males. This is the first report about sexually different responses of poplars in the antioxidant reactions to rust disease. It offers some useful information about the effect of leaf rust on dioecious plants, especially on dioecious woody plants.

The differential response of photosynthesis to high temperature for a boreal and temperate Populus species relates to differences in Rubisco activation and Rubisco activase properties

Hozain, M. I., Salvucci, M. E., Fokar, M., Holaday, A. S. — Wed, 28 Oct 2009 00:18:37 PDT

Significant inhibition of photosynthesis occurs at temperatures only a few degrees (≤ 10 °C) above the optimum, resulting in a considerable loss of potential productivity. Most studies of heat stress have focused on crop or weedy annual plants, whereas similar studies with trees have been limited in number. As temperature is a major factor limiting the geographic ranges of most plants, the aim of this study was to use two Populus species adapted to contrasting thermal environments for determining the factors that constrain photosynthetic assimilation (A) under moderate heat stress in tree species. Consistent with its native range in temperate regions, Populus deltoides Bartr. ex Marsh. exhibited a significantly higher temperature optimum for A than did Populus balsamifera L., a boreal species. The higher A exhibited by P. deltoides at 33–40 °C compared to that for P. balsamifera was associated with a higher activation state of Rubisco and correlated with a higher ATPase activity of Rubisco activase. The temperature response of minimal chlorophyll a fluorescence for darkened leaves was similar for both species and was not consistent with a thylakoid lipid phase change contributing to the decline in A in the range of 30–40 °C. Taken together, these data support the idea that the differences in the temperature response of A for the two Populus species could be attributed to the differences in the response of Rubisco activation and ultimately to the thermal properties of Rubisco activase. That the primary sequence of Rubisco activase differed between the species, especially in regions associated with ATPase activity and Rubisco recognition, indicates that the genotypic differences in Rubisco activase might underlie the differences in the heat sensitivity of Rubisco activase and photosynthesis at moderately high temperatures.

Transient thermal dissipation method of xylem sap flow measurement: multi-species calibration and field evaluation

Tue, 27 Oct 2009 23:27:09 PDT

The transient thermal dissipation (TTD) method developed by Do and Rocheteau (2002b) is a close evolution of the original constant thermal dissipation (CTD) method of Granier (1985). The TTD method has the advantage of limiting the influence of passive natural temperature gradients and of yielding more stable zero-flux references at night. By analogy with the CTD method, the transient method was first calibrated on synthetic porous material (sawdust) on the assumption that the relationship was independent of the woody species. Here, our concern was to test the latter hypothesis with a 10-min heating time in three tropical species: Hevea brasiliensis Müll. Arg., Mangifera indica L. and Citrus maxima Merr. A complementary objective was to compare the field estimates of daily transpiration for mature rubber trees with estimates based on a simplified soil water balance in the dry season. The calibration experiments were carried out in the laboratory on cut stems using an HPFM device and gravimetric control of water flow up to 5 L dm^–2 h^–1. Nineteen response curves were assessed on fully conductive xylem, combining 11 cut stems and two probes. The field evaluation comprised five periods from November 2007 to February 2008. Estimates of daily transpiration from the measurement of sap flow were based on the 41 sensors set up on 11 trees. Soil water depletion was monitored by neutron probe and 12 access tubes to a depth of 1.8 m. The calibrations confirmed that the response of the transient thermal index to flow density was independent of the woody species that were tested. The best fit was a simple linear response (R² = 0.88, n = 276 and P < 0.0001). The previous calibration performed by Do and Rocheteau (2002b) on sawdust fell within the variability of the multi-species calibration; however, there were substantial differences with the average curve at extreme flow rates. Field comparison with soil water depletion in the dry season validated to a reasonable extent the absolute estimates of transpiration acquired with the 10-min TTD method. In conclusion, evidence for the independence of calibration from woody species and the simple linear response of the thermal index strengthen the interest of the TTD method with 10-min heating.

Effects of sample size on sap flux-based stand-scale transpiration estimates

Mon, 12 Oct 2009 02:10:02 PDT

In this study, we aimed to assess how sample sizes affect confidence of stand-scale transpiration (E) estimates calculated from sap flux (F_d) and sapwood area (A_{S_tree}) measurements of individual trees. In a Japanese cypress plantation, we measured F_d and A_{S_tree} in all trees (n = 58) within a 20 x 20 m study plot, which was divided into four 10 x 10 subplots. We calculated E from stand A_{S_tree} (A_{S_stand}) and mean stand F_d (J_S) values. Using Monte Carlo analyses, we examined the potential errors associated with sample sizes in E, A_{S_stand} and J_S using the original A_{S_tree} and F_d data sets. Consequently, we defined the optimal sample sizes of 10 and 15 for A_{S_stand} and J_S estimates, respectively, in the 20 x 20 m plot. Sample sizes larger than the optimal sample sizes did not decrease potential errors. The optimal sample sizes for J_S changed according to plot size (e.g., 10 x 10 and 10 x 20 m), whereas the optimal sample sizes for A_{S_stand} did not. As well, the optimal sample sizes for J_S did not change in different vapor pressure deficit conditions. In terms of E estimates, these results suggest that the tree-to-tree variations in F_d vary among different plots, and that plot size to capture tree-to-tree variations in F_d is an important factor. The sample sizes determined in this study will be helpful for planning the balanced sampling designs to extrapolate stand-scale estimates to catchment-scale estimates.