Abstract
Cell death (CD) may be induced by endogenous or exogenous factors and contributes to all the steps of plant development. This paper presents results related to the mechanism of CD regulation induced by kinetin (Kin) in the root cortex of Vicia faba ssp. minor. To explain the process, 6-(2-hydroxy-3-methylbenzylamino)purine (PI-55), adenine (Ad), 5′-amine-5′-deoxyadenosine (Ado) and N-(2-chloro-4-piridylo)-N′-phenylurea (CPPU) were applied to (i) block cytokinin receptors (CKs) and inhibit the activities of enzymes of CK metabolism, i.e., (ii) phosphoribosyltransferase, (iii) kinases, and (iv) oxidases, respectively. Moreover, ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), lanthanum chloride (LaCl3), ruthenium red (RRed) and cyclosporine A (CS-A) were applied to (i) chelate extracellular calcium ions (Ca2+) as well as blocks of (ii) plasma-, (iii) endoplasmic reticulum- (ER) membrane Ca2+ ion channels and (iv) mitochondria- (MIT) Ca2+ ions release by permeability transition por (PTP), respectively. The measured physiological effectiveness of these factors was the number of living and dying cortex cells estimated with orange acridine (OA) and ethidium bromide (EB), the amounts of cytosolic Ca2+ ions with chlortetracycline (CTC) staining and the intensity of chromatin and Ca2+-CTC complex fluorescence, respectively. Moreover, the role of sorafenib, an inhibitor of RAF kinase, on the vitality of cortex cells and ethylene levels as well as the activities of RAF-like kinase and MEK2 with Syntide-2 and Mek2 as substrates were studied. The results clarified the previously presented suggestion that Kin is converted to appropriate ribotides (5′-monophosphate ribonucleotides), which cooperate with the ethylene and Ca2+ ion signalling pathways to transduce the signal of kinetin-programmed cell death (Kin-PCD). Based on the present and previously published results related to Kin-PCD, the crosstalk between ethylene and MAP kinase signalling, as well as inhibitors of CK receptors and enzymes of their metabolism, is proposed.
Highlights
Cell death (CD) may be induced by endogenous or exogenous factors and contributes to all the steps of plant development
The present results showed that the amounts of cytosolic Ca2+ in the root cortex cells in faba bean seedlings in PI-55–5 and CPPU at 5 μM (CPPU–5) were similar to Kin/PI-55–5 and Kin/CPPU–5, but they were greater in Ad–100 and Ado–50 in comparison with Kin/Ad–100 and Kin/Ado–50
The levels of cytosolic Ca2+ in cortex cells in Kin/La-5, Kin/ruthenium red (RRed)-10 and Kin/cyclosporine A (CS-A)-25 were greater in comparison with cortex of untreated plants (Ctrl) and in Kin series (Figs. 5, 6), but the amounts of Ca2+ in Kin/ EG-10 series were similar to the Ctrl (Fig. 5)
Summary
Cell death (CD) may be induced by endogenous or exogenous factors and contributes to all the steps of plant development. The results indicate that this developmental regulator plays a dual role, i.e., it triggers disruption of some of the destined-to-die cells and simultaneously prevents death in o thers[11]. The latter was evidenced by greater activities of enzymes involved in reactive oxygen. Transmission electron microscopy showed a lack of plasmodesma connections between living and dying cortex cells[11] This is in accordance with data indicating that cytokinins (CKs) are transported by symplasmic connections between cells within p lants[11,14]
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