Search

PubMed: 22974423 It is not known whether tepal senescence in Iris flowers is regulated by hormones. We applied hormones and hormone inhibitors to cut flowers and isolated tepals of Iris × hollandica cv. Blue Magic. Treatments with ethylene or ethylene antagonists indicated lack of ethylene involvement. Auxins or auxin inhibitors also did not change the time to senescence. Abscisic acid (ABA) hastened senescence, but an inhibitor of ABA synthesis (norflurazon) had no effect. Gibberellic acid (GA3) slightly delayed senescence in some experiments, but in other experiments it was without effect, and gibberellin inhibitors [ancymidol or 4-hydroxy-5-isopropyl-2-methylphenyltrimethyl ammonium chloride-1-piperidine carboxylate (AMO-1618)] were ineffective as well. Salicylic acid (SA) also had no effect. Ethylene, auxins, GA3 and SA affected flower opening, therefore did reach the flower cells. Jasmonates delayed senescence by about 2.0 days. Similarly, cytokinins delayed senescence by about 1.5-2.0 days. Antagonists of the phosphatidylinositol signal transduction pathway (lithium), calcium channels (niguldipine and verapamil), calmodulin action [fluphenazine, trifluoroperazine, phenoxybenzamide and N-(6-aminohexyl)-5-chloro-1-naphtalenesulfonamide hydrochloride (W-7)] or protein kinase activity [1-(5-isoquinolinesulfonyl)-2-methylpiperazine hydrochloride (H-7), N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide hydrochloride (H-8) and N-(2-aminoethyl)-5-isoquinolinesulfonamide dihydrochloride (H-9)] had no effect on senescence, indicating no role of a few common signal transduction pathways relating to hormone effects on senescence. The results indicate that tepal senescence in Iris cv. Blue Magic is not regulated by endogenous ethylene, auxin, gibberellins or SA. A role of ABA can at present not be excluded. The data suggest the hypothesis that cytokinins and jasmonates are among the natural regulators. © Physiologia Plantarum 2012.

In extracts from pericarp tissue of ripening tomato (Lycopersicon esculentum Mill. cv, Sonato) fruits, two isoenzymes of polygalacturonase (E.C. 3.2.1.15), PG1 and PG2, are usually found. Also in such extracts, or as part of PG1, a convertor (CV) occurs. Incubation of PG2 with this CV gives rise to PG1 or a different isoenzyme, PGx, that is also stable at 65°C but differs in pH optimum and size from PG1. It appears that CV has two affinity sites that can bind with PG2 or with a polydextran. PG1 is an extraction artifact, consisting of one molecule of CV and two molecules of PG2. PGx is made up of one molecule of CV and one molecule of PG2. It is the CV part of PGx that binds to polydextrans such as Blue Dextran 2000, Sephadex G-100, and cell wall preparations. In this last form PGx is the physiologically active form of the enzyme, solubilizing demethylated pectin. On Sephacryl S-300, CV appears to have a molecular weight of 81 kDa, but because of its heat stability and partial leakage through a 10 kDa cut-off membrane, it might be a much smaller, rod-like molecule. The polygalacturonase convertor might be a lectin without intrinsic enzyme activity, with a function to immobilize, stabilize and activate enzymic proteins in the cell wall.

asterisk inside a circle sign Visible senescence of the flag tepals in Iris x hollandica (cv. Blue Magic) was preceded by a large increase in endoprotease activity. Just before visible senescence about half of total endoprotease activity was apparently due to cysteine proteases, somewhat less than half to serine proteases, with a minor role of metalloproteases. asterisk inside a circle sign Treatment of isolated tepals with the purported serine protease inhibitors AEBSF [4-(2-aminoethyl)-benzenesulfonyl fluoride] or DFP (diisopropyl-fluorophosphate) prevented the increase in endoprotease activity and considerably delayed or prevented the normal senescence symptoms. asterisk inside a circle sign The specific cysteine protease-specific E-64d reduced maximum endoprotease activity by 30%, but had no effect on the time to visible senescence. Zinc chloride and aprotinin reduced maximum endoprotease activity by c. 50 and 40%, respectively, and slightly delayed visible senescence. A proteasome inhibitor (Z-leu-leu-Nva-H) slightly delayed tepal senescence, which indicates that protein degradation in the proteasome may play a role in induction of the visible senescence symptoms. asterisk inside a circle sign It is concluded that visible senescence is preceded by large-scale protein degradation, which is apparently mainly due to cysteine- and serine protease activity, and that two (unspecific) inhibitors of serine proteases considerably delay the senescence symptoms.

Summary When cut flowering stems of roses ( Rosa hybrida L. ‹Sonia›), Bouvardia hybrid #x2039;Artemis Jowhite› and Astilbe hybrid #x2039;Cattleya#x203A; were held dry for 24 h at 20#x00B0;C and 60% r.h., an occlusion for water uptake developed in the lowermost segment of the stems_ When placed in water after dry storage, the flowering rose stems showed a small increase in fresh weight (FW), the stems of Bouvardia no increase in FW, and the Astilbe stems a decrease in FW. Placement of the stems in an aqueous solution containing a surfactant (Nonoxynol-8.5), prior to exposure to air, resulted in a marked increase in FW in all three investigated species when the stems were placed in watar after exposure to air. This increase in FW was not due to a reduction in the rate of transpiration during exposure to air, but to an increase in water uptake during the first day after the exposure to air. The results indicate that the occlusion is related to surface tension. Three alternative mechanisms involving surface tension are discussed.

In onion (Allium cepa L.) postponement of sprouting is necessary to achieve long term storage. We studied the factors determining sprouting during dry storage at 16°C. The period to visible sprouting depends on the length of the dormancy period, if present, and on the growth rate of the sprout. In the three cultivars tested, sprouts were initiated within 2 weeks after harvest indicating the absence of a real dormancy period. Sprout length increased linearly during storage. The mitotic activity of the apex decreased before harvest, was low at the transition from scale to leaf formation, and increased again when the sprout was initiated. From a few weeks before harvest, the initially high fructan content of the scales decreased, leading to a large increase in fructose. The sprout always contained enough carbohydrates for growth (between 50 and 60 mg g-' dry weight, of which 30% was fructan). The activity of sucrose synthase (EC 2.4.1.13) increased as the sprout grew, indicating an increase in sink strength. Invertase (EC 3.2.1.26) was absent in all bulb organs, during the various developmental stages. Although carbohydrates and enzymes were available for fast sprouting, sprout growth was still linear instead of exponential during dry storage at temperatures favorable for growth (16°C). The relative importance of factors determining sprouting are discussed.

Iris x hollandica (cv. Blue Magic) flowers show the first symptoms of senescence within 4 days after the onset of flower opening. Wilting of the tepals starts at the distal edges, rapidly proceeds to the base, and is followed by total discolouration of the tepal. Senescence of Iris flowers is not induced or promoted by ethylene, the hormone often involved in senescence processes in plants. Whether other signals trigger cell death in Iris flowers is still unknown. The senescence process of Iris tepals is characterized by specific changes on the cellular level prior to the visible symptoms. Mesophyll cells show the presence of organelle désintégration, except for mitochondria, and their subsequent autophagic lysis in vacuoles. The vacuoles, in turn, deteriorate when they have emptied most of the cytoplasm and digested its constituents. The total protein and phospholipid content of the tepals decreases dramatically. At a later stage the plasma membrane loses its integrity, resulting in leakage of cellular contents and loss of turgor, which is accompanied by tepal wilting. The decrease in protein levels seems mainly the result of increased protein degradation by protease activity. Membrane degradation and decreased phospholipid contents could be caused by a concerted action of enzymes with lipase activity. Phospholipase D (PLD) may initiate phospholipid degradation in plants, as it has high abundance and because of the lipid degradation products found. Since PLD activity can be regulated on a transcriptional and post-translational level, an in vivo assay for monitoring PLD activity was developed. An early increase in PLD activity was observed, which correlated well with a decrease in phospholipid content. The results, therefore, strongly indicate that PLD is involved in membrane degradation associated with tepal senescence.