Cell wall acidification in growing barley (Hordeum vulgare L.) leaves

Apoplast acidification associated with growth is well-documented in roots and coleoptiles but not in leaves. In the present study, advantage was taken of high cuticle permeability in the elongation zone of barley leaves to measure apoplast pH and acidification and the role which the plasma membrane H+ ATPase (PM-ATPase) plays in this process. An in-vitro gel system and pH-microelectrodes were used to monitor pH, and growth was measured with a linear variable differential transformer (LVDT). Test reagents which blocked (vanadate) or stimulated (fusicoccin) PM-ATPase were applied to the leaf elongation zone. In addition, the expression level (qPCR) and activity of PM-ATPase was determined. Apoplast pH was lower in growing compared with non-growing tissue. Growth and apoplast acidification were stimulated by fusicoccin and reduced by vanadate. Expression of PM-ATPase, as judged from Ct-values, was almost identical in the two leaf regions. In contrast, activity of PM-ATPase, expressed per unit plasma membrane protein, was about twice as high in growing tissue. It is concluded that PM-ATPase is required in growing leaf cells to achieve maximum rates of elongation and apoplast acidification and that this is due in part to a higher plasma membrane surface density of PM-ATPase activity

Recent advances in understanding of the mechanism of paraquat resistance

Cationic amino acid/polyamine transporter CAT4 is supposed to play essential part in paraquat resistance of horseweed. In order to get better understanding on its role in resistance mechanism here we examined and compared the expression level of this transporter in the susceptible rape Brassica napus and in the different (susceptible and resistant) biotypes of horseweed. We found that paraquat induced an increase in expression level of CAT4 in rape, similarly to its upregulation in horseweed

Apoplast acidification in growing barley (Hordeum vulgare L.) leaves

Apoplast acidification associated with growth is well-documented in roots, coleoptiles and internodes but not in leaves. In the present project on barley (Hordeum vulgare L.) advantage was taken of the high cuticle permeability in the elongation zone of leaves to measure apoplast pH and growth in response to application of test reagents. The role of the plasma membrane H+-ATPase (PM-H+-ATPase) and K+ in this process was of particular interest. An in vitro gel system with bromocresol purple as pH indicator, pH microelectrodes and pH-sensitive fluorescence dye combined with confocal microscopy were used to monitor apoplast pH. Growth was measured in parallel or in separate experiments using a linear variable differential transformer (LVDT). Test reagents which blocked (vanadate) or stimulated (fusicoccin) PM-H+-ATPase, or which reduced (NH4 +, Cs+, tetraethylammonium) K+ uptake were applied. Plasma membranes were isolated from growing and mature leaf tissue and used to determine the activity (ATPase assay) and abundance (Western blotting) of PM-H+-ATPase protein. Protein localisation was studied by immunohistochemistry and expression of mRNA quantified using real time PCR (qPCR). Apoplast pH was by up to 1.0 pH unit lower in growing compared to nongrowing leaf tissue. Depending on the K+ concentration in the bathing medium used during electrophysiological analyses, apoplast pH in the elongation zone ranged from pH 4.8 (0.1 mM K+) to pH 5.8 (10 mM K+). In the emerged blade, apoplast pH remained at about pH 5.8 irrespective of the K+ concentration in the bathing medium Growth was more responsive to test reagents than to changes in apoplast pH. Expression of PM-H+- ATPase was comparable between growing and non-growing leaf regions when expression was related to per unit extracted RNA or cell number. However, when expression was related to per unit surface area of plasma membrane, expression of PM-H+-ATPase was about twice as high in growing compared to non-growing leaf tissue. The same applied to the protein level and activity of PM-H+-ATPase. Immunohistochemical analyses showed that PM-H+-ATPase was present in all living leaf tissues, particular in those (guard cells, phloem, and xylem parenchyma) associated with high rates of trans-membrane solute transport. It is concluded that leaf cell expansion in barley depends on the activity of the PM-H+-ATPase and K+ transport processes. The higher surface density of PM-H+-ATPase activity in growing barley leaf tissue aids apoplast acidification and growth. A H+ / K+ co-transport system may play a key role in linking growth with apoplast pH, H+ pump activity and K+-uptake

Mechanoreceptor sejtek a Mimosa pudica tercier pulvinusán

Annak ellenére, hogy feltűnően gyors mozgása miatt a Mimosa pudica kedvelt kísérleti objektum, mégis sok vele kapcsolatban a megválaszolatlan kérdés. Máig sem sikerült megtalálni azokat a mechanoreceptor sejteket, melyek érzékelik a külvilágból érkező mechanikai jeleket és továbbítják a növény felé. Munkánk során a növény tercier pulvinusán ilyen mechanoreceptív sejteket fedeztünk fel. Megfigyeltük ezeknek a sejteknek a fény- és elektronmikroszkópos szerkezetét, igyekeztünk felderíteni a receptor sejtek és az azok közelében lévő szomszédos sejtek között meglévő sejt-sejt kapcsolatokat is. Elektrofiziológiai vizsgálataink igazolták, hogy az általunk felfedezett sejtek mechanikai ingerek segítségével ingerületbe hozhatók, és a keletkező akciós potenciálok tovaterjedve alkalmasak a levelek mozgatását végző motorsejtek irányítására