Carbon balance in leaves of young poplar trees.

In the present study, important components of carbon metabolism of mature leaves of young poplar trees (Populus x canescens) were determined. Carbohydrate concentrations in leaves and xylem sap were quantified at five different times during the day and compared with photosynthetic gas exchange measurements (net assimilation, transpiration and rates of isoprene emission). Continuously measured xylem sap flow rates, with a time resolution of 15 min, were used to calculate diurnal balances of carbon metabolism of whole mature poplar leaves on different days. Loss of photosynthetically fixed carbon by isoprene emission and dark respiration amounted to 1% and 20%. The most abundant soluble carbohydrates in leaves and xylem sap were glucose, fructose and sucrose, with amounts of approx. 2 to 12 mmol m(-2) leaf area in leaves and about 0.2 to 15 mM in xylem sap. Clear diurnal patterns of carbohydrate concentration in xylem sap and leaves, however, were not observed. Calculations of the carbon transport rates in the xylem to the leaves were based on carbohydrate concentrations in xylem sap and xylem sap flow rates. This carbon delivery amounted to about 3 micromol C m(-2) s(-1) during the day and approx. 1 micromol C m(-2) s(-1) at night. The data demonstrated that between 9 and 28 % of total carbon delivered to poplar leaves during 24 h resulted from xylem transport and, hence, provide a strong indication for a significant rate of carbon cycling within young trees.

Oxidative pentose phosphate pathway and pyridine nucleotides in relation to heartwood formation in Robinia pseudoacacia L.

Most tree species show in the inner parts of their woody axes often a dark colored zone, the heartwood. Its formation is a genetically determined, programmed cell death which is characterized by the activation of metabolic pathways which lead to the formation of phenolic heartwood extractives. In the present paper we report on the key position of the oxidative pentose phosphate pathway (OPP) for this process. The OPP plays a crucial role in anabolic processes and is involved in the interconversion and rearrangements of sugar-phosphates with the net production of NADPH. In tissues of Robinia pseudoacacia L. which are transferred to heartwood, enhanced activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) are present. A consequence of these increased enzyme activities is a shift in the pyridine nucleotide pool towards NADP+NADPH at the expense of NAD+NADH. These alterations in the metabolism and the redox status probably provide precursors and reduction equivalents being required for the synthesis of heartwood phenolics. The non heartwood forming species Acer pseudoplatanus L. shows neither a radial gradient nor seasonal changes in the amounts of pyridine nucleotides across the trunkwood. The results are discussed in connection with programmed cell death, mitochondrial activity, and heartwood formation.

Function and dynamics of auxin and carbohydrates during earlywood/latewood transition in scots pine.

In temperate regions the annual pattern of wood development is characterized by the formation of radially narrow and thick walled latewood cells. This takes place at the later part of the growing season when cambial cell division declines. To gain new insight into the regulation of this process, micro-analytical techniques were used to visualize the distribution of indole-3-acetic acid (IAA), soluble carbohydrates, and activities of sucrose (Suc)-metabolizing enzymes across the cambial region tissues in Scots pine (Pinus sylvestris). The total amount of IAA in the cambial region did not change with latewood initiation. But its radial distribution pattern was altered, resulting in an increased concentration in the cambial meristem and its recent derivatives. Thus, initiation of latewood formation and cessation of cambial cell division is not a consequence of decreased IAA concentrations in dividing and expanding cells. Rather, IAA most likely has a role in defining the altered developmental pattern associated with latewood formation. Carbohydrates and enzyme activities showed distinctive radial distribution patterns. Suc peaked in the phloem and decreased sharply to low levels across the cambial zone, whereas fructose and glucose reached their highest levels in the maturing tracheids. Suc synthase was the dominating Suc cleaving enzyme with a peak in the secondary wall-forming tracheids and in the phloem. Soluble acid invertase peaked in dividing and expanding cells. Suc-phosphate synthase had its highest activities in the phloem. Activities of cell wall bound invertase were low. The absence of major seasonal variations indicates that carbohydrate availability is not a trigger for latewood initiation. However, steep concentration gradients of the sugars suggest a role for sugar signaling in vascular development.

Ecophysiological responses of Empetrum nigrum to heavy metal pollution.

Chlorophyll, organic (citric and malic acids) and abscisic acid (ABA) contents and stem water potential were measured to indicate possible physiological effects of heavy metal deposition on Empetrum nigrum L. (crowberry). The leaves and stems of E. nigrum were collected at distances of 0.5 and 8 km from the Cu-Ni smelter at Harjavalta, south-west Finland. All the investigated parameters were clearly affected by heavy metal emissions. Chlorophyll contents in the leaves and organic acid contents in the leaves and stems were lower close to the emission source. Generally found increase in organic acid contents with increasing Ni concentrations was not found, which might be due to the lower production of organic acids measured by decreased photosynthesis near the smelter. In contrast, ABA contents in stems and leaves in general, were higher in plants growing 0.5 km from the pollution source. Close to the smelter the stem water potential of E. nigrum was less negative during the day but more negative during the night. These results suggest that smelter emissions have a negative effect on the ecophysiology of E. nigrum even though it is considered to be a tolerant species to heavy metals.

Alteration of physiological parameters in needles of cloned spruce trees (Picea abies (L.) Karst.) by ozone and acid mist.

Three-year-old clonal spruce trees, kept in growth chambers, were treated with ozone and acid mist during a period of 14 months. One half of the trees were grown on an acidic sandy soil, the other half on a calcareous soil rich in carbonate. At the end of the fumigation period, carbohydrates (glucose, fructose, sucrose, raffinose, starch, glucose-1-phosphate and fructose-6-phosphate) and parameters of the energy status (ATP-, AdN-(ATP + ADP + AMP)- levels, ATP/ADP-ratios and adenylate-energy-charge-(AEC)-values) were determined in the current-year's needles. The results indicate that the metabolic status of a plant tissue is not only influenced by the nature of the air pollutants. Soil factors play an important role in metabolic changes within the plant and are thus of relevance in the manifestation of damage symptoms.

Pig brain homogenates contain smooth muscle myosin and cytoplasmic myosin isoforms.

Three myosin isoforms, two of smooth muscle and one of cytoplasmic origin, were found in porcine brain by Western blotting analysis with antibodies specific for smooth and cytoplasmic myosins. The smooth muscle isoforms comprise at least 30% of the total myosin present. Brain tissue is therefore not a suitable source for the isolation of pure cytoplasmic contractile proteins.

Histones bind to contractile proteins and inhibit actomyosin ATPase.

Nuclear histones bind to and precipitate the major contractile proteins, actin and myosin. The binding of histone to actin seems to reach saturation at 2:1 ratio, the interaction may serve some regulatory function(s) in intranuclear events. The binding of histone to myosin is not saturable, and, although it inhibits the actin-activated Mg2+-dependent myosin ATPase activity, does therefore not seem of physiological importance.