New Phytologist

doi: 10.1111/j.1469-8137.1994.tb07522.xpmid: N/A

CAIRNS, ANDREW J.; ASHTON, JENNIFER E.

doi: 10.1111/j.1469-8137.1994.tb07523.xpmid: N/A

A crude enzyme preparation from excised illuminated leaves of Lolium temulentum L. catalyzed the de novo synthesis of fructan of apparent degree of polymerization 3–20.

CANNY, M.J.; HUANG, C.X.

doi: 10.1111/j.1469-8137.1994.tb07524.xpmid: N/A

The rate at which solutes may move in the cell wall apoplast of roots was assessed by measuring the diffusivity (D) of a dye, sulphorhodamine G (SR), in freshroots of field‐grown maize. Pieces of axile and branch roots from regions with soil sheaths (with immature late metaxylem) and without sheaths (with mature late metaxylem) were placed in SR solution for 5, 20 and 80 min, removed, rinesed and freeze‐substituted. The water‐soluble SR was retained in position in the tissues during anhydrous embedding and sectioning. The distance of radial penetration of the dye was measured from micrographs taken in the fluorescence microscope. Fick's aecond law was used to calculate values of D. The values are expressed relative to the value of D in water (Daq). Mature axile roots uniformly gave values of D=Duq/1000. In immature axile roots D varied from 0 (no penetration through the hypodermal walls) through Duq/1000 to D aq/40 (the maximum value found). This variation probably arises from a developmental sequence. with D high in the region to 10 cm from the tip. zero in the region 10‐25 cm from the tip, and low further back (merging with values for mature roots). In branches of both immature and mature roots also, D was highly variable, from zero to Daq/40. SR was found to penetrate through the endodermis of axes and branches, following sub‐microscopic paths around the lining of pits in the secondary walls. It is concluded that soil solutes probably enter roots at the outermost layer of cells, and that the cell wall apoplast is most unlikely to be a path for flowing water.

WANG, X. L.; McCULLY, M. E.; CANNY, M. J.

doi: 10.1111/j.1469-8137.1994.tb07525.xpmid: N/A

The late metaxylem (LMX) in the first‐order branch roots of maize matures slowly. Fully lignified elements remain as individual cells of mean diameter 67 μm and length about 2 mm for considerable distances proximal from the tip of branches that retain an active meristem (indeterminate branches). Such branches, depending on their age, have from 0 to 45%, of the Total length of LMX conduits mature and open for unrestricted conduction of the transpiration stream. In determinate branches (those that have lost their meristem), up to 60% of LMX length is open for conduction. The closed portion of the xylem conduits is at the distal end of the branches. In both indeterminate, and the youngest determinate branches, immature, living xylem elements provide the block in the conduits. Later, progressive decay in the determinate branches passes basipetally beyond the immature elements, bus the distal ends of the conduits remain closed, plugged initially by mucilaginous materials apparently of root origin, and subsequently by invading microbes. It is proposed that the closed ends of the xylem conduits restrict leakage from the more proximal regions, and also prevent their blockage by embolisms. The presence of mature LMX conduits open for unrestricted water conduction is consistent with the major role in water uptake assigned to the branch roots in earlier studies.

BIRADAR, D. P.; RAYBURN, A. LANE

doi: 10.1111/j.1469-8137.1994.tb07526.xpmid: N/A

Nuclei were isolated from stems, mesocotyls, nodal roots and root tips of two maize hybrids. The fluorochrome, propidium iodide (PI), was used to stain the nuclei that were passed through a flow cytometer‐cell sorter. Significant differences in fluorescence intensities were observed among the diploid nuclei from the different plant organs. These observations, in conjunction with previously reported DAPI fluorescence data, reflect the state of chromatin condensation in diploid nuclei isolated from meristematic and differentiating tissues. Nuclei from root meristematic tissues showed no or very little chromatin condensation. Mesocotyls and nodal roots, 1‐wk‐old, appeared to contain chromatin in a more diffuse state owing to completed differentiation which allows more DNA to be accessible to PI. Mesocotyls, 2‐wk‐old owing to senescence, contained degraded chromatin in which DNA was more accessible to PI because it lacked associated proteins. The diploid nuclei from stems had the highest amount of chromatin condensation. The results show the usefulness of flow cytometry for analyzing chromatin condensation in plant nuclei. The study also shows the importance of selecting a particular type of fluorochrome in the analysis of nuclear chromatin.

HERNÁNDEZ, JOSE A.; DEL RÍO, LUIS A.; SEVILLA, FRANCISCA

doi: 10.1111/j.1469-8137.1994.tb07527.xpmid: N/A

The effect of salt stress (NaCl and/or KCl) on the specific activity of superoxide dismutase (SOD) isozymes in leaves from cowpea plants and in mesophyll protoplasts from cowpea leaves was examined. In leaves, mitochondrial Mn‐SOD was significantly decreased by 35 mM (up to 35%) and 100 mM NaCl (up to 60%), whereas, under the same conditions, cytosolic and mitochondrial Cu, Zn‐SOD I was slightly diminished and chloroplastic Cu, Zn‐SOD II did not show a response. In protoplasts, the specific activity of SOD isozymes was decreased as a function of both the salt concentration and the type of salt used Mn‐SOD was again the most salt‐sensitive isozyme, but in contrast to whole leaf preparations. Cu, Zn‐SOD II in protoplasts was markedly inhibited by NaCl and Cu, Zn‐SOD I showed an intermediate sensitivity. KCl concentrations equivalent to those of NaCl were less effective in inhibiting the SOD isozymes, suggesting the existence of specificity for certain ions. In protoplasts salt inhibition of SODs was reversible. However, Mn2+ was necessary for total recovery of Mn‐SOD activity in NaCl‐treated protoplasts. The in vitro results suggested a competitive inhibition of SOD isozymes by salts. A possible competitive inhibition of SOD activity in salt‐treated cowpea plants was also suggested. Finally, the possible correlation between plant response to NaCl and the potential of SOD isozymes was analyzed.

CAPORN, S. J. M.; HAND, D. W.; MANSFIELD, T. A.; WELLBURN, A. R.

doi: 10.1111/j.1469-8137.1994.tb07528.xpmid: N/A

The canopy net photosynthesis (Pn) of lettuce (Lactuca sativa L. ev.‘Ambassador’) was analyzed under controlled conditions simulating the winter glasshouse atmosphere. Prior to measurements the plants were grown in CO2‐enriched air of 1000 μmol mol−1, at a photosynthetic photon flux density (PPFD) of 280 μmol m2 s−1 (400–700 nm) and a day/night air temperature of 16/13 °C.

PANDEY, J.; AGRAWAL, M.

doi: 10.1111/j.1469-8137.1994.tb07529.xpmid: N/A

A two‐year study was conducted in the urban environment of Varanasi, India, to evaluate plant responses to urban air pollution. Three species including a shrub (Carissa carandas L.) and two tree species (Delonix regia Rafin and Cassia fistula L.) were grown in pots at selected study sites. Changes in plant performance were considered in relation to the status of ambient air quality.

FANGMEIER, A.; BRUNSCHÖN, S.; JÄGER, H.‐J.

doi: 10.1111/j.1469-8137.1994.tb07530.xpmid: N/A

Protein content, catalase activity (CAT), non‐specific peroxidase activity (POD), ascorbic acid content (AsA) and malondialdehyde content (MDA) were estimated in flag leaves of spring wheat exposed to ozone and drought stress in open‐top chambers. Four harvests were carried out at different developmental stages to estimate the time course of these parameters. Senescence was enhanced by ozone which was reflected in the time course of the oxidant stress biomarkers. Protein content decreased, and POD and MDA increased only after the leaves had experienced high doses of ozone, whereas AsA levels were raised in ozone‐treated plants after only a short exposure period. CAT did not significantly respond to ozone treatment, but, ozone accelerated the progress of its time course. Drought stress did not influence the time course of any of the estimated parameters, but led to somewhat increased levels of AsA.

BOSAC, C.; ROBERTS, J. A.; BLACK, V. J.; BLACK, C. R.

doi: 10.1111/j.1469-8137.1994.tb07531.xpmid: N/A

The flowering racemes of Brassica napus L. cv. Tapidor were exposed independently from the vegetative component to 200 nl l−1, 100 nl l−1 O3/30 nl l−1 SO2, In all cases, a single 6 h exposure significantly increased bud abortion, and abscission 2 and 5 d after treatment. Similar results were obtained using cv. Libravo, although the effect of 100 nl l−1 O3 was significant only after 2 d. Exposure to 30 nl l−1 SO2 did not enhance bud abortion and abscission in either variety. Longer term measurements for up to 25 d revealed a trend to wards sustained losses of fertile sites in those pollutant treatments which had exhibited demonstrable, effects after 2 and/or 5 d. However, the number of fertile sites present was comparable to or even higher than in the controls, indicating that compensation for the initial losses must have occurred. Following exposure, plants of cv. Tapidor tended to develop longer total raceme lengths and greater numbers of raceme branches, and those of cv. Libravo a greater number of raceme branches. Indicating possible methods by which new fertile sites may have been produced. The significance of these observations for the reproductive development of field‐grown oilseed rape is discussed.