Annick Hourmant

Effects of Interaction between Polyamines and Benzyladenine on Betacyanin Synthesis in Amaranthus Seedlings

Summary The synthesis of betacyanin in Amaranthus cotyledons is a cytokinin dependent process and forms a sensitive bioassay to study interactions between polyamines and cytokinins. Treatment with benzyladenine or diamines (putrescine and diaminopropane) increased the betacyanin content 1.5- to 2.5-fold. In contrast to diamines, spermidine and spermine depressed the synthesis of the pigment. Furthermore, when benzyladenine was applied simultaneously with polyamines, it reinforced the effects of putrescine and counteracted the inhibition due to spermidine and spermine. When seedlings were treated with benzyladenine, the endogenous level of putrescine, spermidine and spermine was raised by 27-36%. The addition of Difluoromethylornithine (DFMO) and Difluoromethylarginine (DFMA) to benzyladenine prevented the rise in betacyanin and polyamine contents. These results seem to favour a participation of polyamines in benzyladenine-dependent betacyanin synthesis but suggest that exogenous spermidine and spermine could have non specific-effects.

Influence of Abscisic acid on K+ absorption by leaf discs ofSolanum tuberosum

It is shown that, contrary to what is generally found, treatment with abscisic acid (ABA) of potato leaf tissues resulted in an increase of K+ uptake. Comparison with other hormones was made: BAP induced an inhibition and GA3 a stimulation of K+ uptake. The uptake was sensitive to several metabolic inhibitors, external pH and ATPase inhibitors while p-chloromercuribenzenesulfonic acid (PCMBS) had no effect. Uptake kinetics revealed the presence of both saturable and linear components which were both stimulated by ABA treatment. Our data are consistent with an effect of ABA on the active and passive components of K+ uptake. These results are discussed in relation to the action of ABA on foliar senescence and the action on ion partitioning in the whole plant.

Long distance transport of 14C-putrescine in potato plantlets (Solanum tuberosum cv. Bintje)

Summary Polyamines can be considered as a new class of plant growth regulators. However to be considered as hormones, they have to respond to the translocatability criterion in the whole plant. The results presented here show that a small droplet (10 µl) of 14 C-putrescine supplied to a source leaf is redistributed to the whole plant. Long-distance transport occurs mainly towards young growing organs (apex, roots, stolons, tubers). Bidirectional translocation, which is also found is a result of interactions between the attractive strengths of different sinks. Heat girdling of shoots induces a strong inhibition of transport which suggests transport via the phloem. Other data, such as non labeling of mature leaves, normally fed by xylem flux and the higher content (4 to 10 times) of endogenous PA s in phloem exudate compared with xylem exudate confirm this conclusion. After a 3 h period of transport, separation of labelled compounds by thin layer chromatography shows that the radioactivity supplied as 14 C-putrescine is found as putrescine (from 64% to 82%), spermidine (from 14% to 28%) and spermine (3%) depending on the organ. This indicates that there is no important degradation of putrescine before it reaches the transport pathway.

Influence de i’acide abscissique sur le transport d’ions inorganiques chez la pomme de terre (solanum tuberosum cv. Bintje). etude comparée avec quelques autres phytohormones

Using detached leaves of potato plants (Solanum tuberosum cv. Bintje) it was shown that abscisic acid (ABA) induced an oriented transport of ions (86Rb,32P and3SS) towards the hormone-treated leaflet. In order to understand the hormone effect on cell permeability, pretreatment of discs with hormonal solution was conducted. The pretreatment with ABA stimulated the uptake of K+ simultaneously with the decrease of efflux.The effect of ABA on ion uptake is compared with the action of other hormones, benzylaminopurine (BAP), gibberellic acid (GA3) known to act over a long distance transport, too.Three kinds of specificity are underlined: - hormonal specificity (stimulation by ABA and inhibiton by BAP of K+ uptake by foliar tissues); - ionic specificity (ABA increase86Rb influx, but inhibits32P and3SS influx); - tissue specificity shown by a comparative study between foliar tissues (source) and tuber tissues (sink). The autoradiography of foliar discs demonstrated that a treatment of foliar discs can be used, at least for Rb+ (K), to study role of ABA in long-distance transport.

Contribution à l’étude de làabsorption du saccharose par des tissus de tubercule de pomme de terre adulte (Solatium tuberosum L.) modalités et influence des phytohormones

Sugar uptake by potato tuber discs was studied. Discs were used “fresh” or after a 24-h ageing period. It was shown that ageing increases (by 3 to 4 times) the rate of glucose and sucrose uptake. Sucrose uptake by fresh tissues was insensitive to the presence of glucose or fructose while a competitive effect was observed after ageing. This indicates the development of an invertase activity, which was inhibited by tris-buffer. Sucrose and glucose uptake by aged discs was dependent on cellular metabolism as shown by the sensitivity to low temperature and metabolic inhibitors (NaCN, DNP, CCCP). Involvement of thiol groups was demonstrated by the inhibition with NEM and PCMBS. Orthovanadate, which decreases phosphate uptake by 85 % (Poderet al. 1986) did not produce any effect on glucose and sucrose uptake by aged tissues. Fusicoccin produced only a slight stimulation (15 %). These results argue in favour of the involvement of specific ATPases in ion and sugar uptake. No involvement of a redox system was observed. ABA and BAP inhibited the uptake induced by ageing but had no effect on the endogenous sugar content. BAP would act by its effect on the amount of ATP while ABA would act at the membrane level. The results are discussed in relation to the mechanisms of transfer of glucosyl groups and to the transport of sucrose by the symplasmic pathway. Reçule

Cycle cultural et floraison de l'échalote, Allium cepa L. var aggregatum (cvs Mikor et Jermor)

Summary The flowering percentage and the number of flowering stems per bulb of “Mikor and” Jermor, two clones of Jersey shallot (Allium cepa L. var. aggregatum) cultivated in field, were assessed during two growing seasons, in relation with bulb storage conditions and the planting date. When “Jermor bulbs were planted in mid—october after storage at ambiant temperature or at 30°C, they exceptionally flowered. Under the same conditions, “Mikor expressed a high percentage of flowerind and the bulb bears numerous buds that flower in a random and independent way. The storage of “Mikor bulbs at 30°C, before an october planting, intensifies blooming but after planting, i.e. in december or february, it strongly reduces and finally suppresses flowering. These data during two successive years suggest that blooming is preceded by a sequence of physiological states which the bulbs must run through late planting in the field and the lack of cold after planting would be unfavourable conditions for “Mikor flowering and...

Influence of Abscisic Acid on K+ absorption by leaf tissues ofSolanum tuberosum L. (cv. Bintje). Relation with calcium fluxes and with calmodulin

Previous results with potato leaf tissues revealed that a treatment with ABA (10-4 M) induced an increase of K+ uptake (Suleimanet al., 1990a).In this study, we investigate the relationship between increased K+ uptake, Ca2+ fluxes and calmodulin by treating potato leaf discs with Ca2+ channel blockers (La3+, verapamil and nifedipine) and with calmodulin inhibitors (chlorpromazine, W7: N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide, and compound 4880).We found : a) all these inhibitors decreased K+ uptake in the same ratio in tissues treated or not with ABA; b) a synergistic effect between ABA and the Ca2+ ionophore A 23187 on K+ uptake.The results suggest that the hormone may act on K+ uptake like a Ca2+ agonist, in accord with HUDDART’s hypothesis.

Involvement of catecholic compounds in morphogenesis of in vitro potato plants effect of methylglyoxal-bis (guanylhydrazone)

Summary The occurrence and amount of catecholic compounds in potato vitroplants ( Solanum tuberosum L. cv. Bintje) during growth were investigated. Biogenic amines such as 3,4-dihydroxyphenylalanine (DOPA), dopamine and 2 other catecholic compounds, namely caffeic acid and protocatechuic aldehyde, have been identified and quantified with high sensitivity by high performance liquid chromatography with electrochemical detection, following selective extraction. These molecules are present in all parts of the plants and their content (DOPA, dopamine, caffeic acid) increases parallel to growth; caffeic acid is mainly concentrated in tubers while leaves are the richest organs in dopamine. Addition of exogenous dopamine to the culture medium caused a great stimulation of growth, especially of aerial parts. When methylglyoxal-bis(guanylhydrazone) (MGBG), an inhibitor of spermidine biosynthesis, was added to the culture medium, it produced morphogenetic effects that are correlated to changes in dopamine amount. This inhibitor decreased the dopamine content of aerial parts when it inhibited their growth and enhanced this catecholic compound in tubers when it stimulated their development; MGBG also produced a large increase in caffeic acid, probably linked to the stimulation of conjugated polyamines previously shown in tubers. These results support the hypothesis that catecholic compounds are involved in the morphogenesis of potato plants.

Influence of abscisic acid on the transport of ions in potato (Solanum tuberosum cv. Bintje). Comparative study with some other phytohormones.

Using detached leaves of potato plants (Solanum tuberosum cv. Bintje) it was shown that abscisic acid (ABA) induced an oriented transport of ions (86Rb,32P and3SS) towards the hormone-treated leaflet. In order to understand the hormone effect on cell permeability, pretreatment of discs with hormonal solution was conducted. The pretreatment with ABA stimulated the uptake of K+ simultaneously with the decrease of efflux.The effect of ABA on ion uptake is compared with the action of other hormones, benzylaminopurine (BAP), gibberellic acid (GA3) known to act over a long distance transport, too.Three kinds of specificity are underlined: - hormonal specificity (stimulation by ABA and inhibiton by BAP of K+ uptake by foliar tissues); - ionic specificity (ABA increase86Rb influx, but inhibits32P and3SS influx); - tissue specificity shown by a comparative study between foliar tissues (source) and tuber tissues (sink). The autoradiography of foliar discs demonstrated that a treatment of foliar discs can be used, at least for Rb+ (K), to study role of ABA in long-distance transport.

Influence de i’acide abscissique sur le transport d’ions inorganiques chez la pomme de terre (solanum tuberosum cv. Bintje). etude comparée avec quelques autres phytohormones: Laboratoire de physiologie végétale, faculté des sciences et techniques, 6. avenue lc gorgeu 29287 Brest Cédex, France Influence of Abscisic Add on the Transport of Inorganic Ions in Potato (Solanum tuberosun cv. Bintje). Comparative Study with Some Other Phytohormones

Using detached leaves of potato plants (Solanum tuberosum cv. Bintje) it was shown that abscisic acid (ABA) induced an oriented transport of ions (86Rb,32P and3SS) towards the hormone-treated leaflet. In order to understand the hormone effect on cell permeability, pretreatment of discs with hormonal solution was conducted. The pretreatment with ABA stimulated the uptake of K+ simultaneously with the decrease of efflux.The effect of ABA on ion uptake is compared with the action of other hormones, benzylaminopurine (BAP), gibberellic acid (GA3) known to act over a long distance transport, too.Three kinds of specificity are underlined: - hormonal specificity (stimulation by ABA and inhibiton by BAP of K+ uptake by foliar tissues); - ionic specificity (ABA increase86Rb influx, but inhibits32P and3SS influx); - tissue specificity shown by a comparative study between foliar tissues (source) and tuber tissues (sink). The autoradiography of foliar discs demonstrated that a treatment of foliar discs can be used, at least for Rb+ (K), to study role of ABA in long-distance transport.