J. Krekule

Reversal of IAA-induced inhibition of flowering by aminoethoxyvinylglycine inChenopodium

Aminoethoxyvinylglycine (AVG) applied as a droplet (3 μl, 0.1 mM) to the plumule of seedlings of both the short-day plantChenopodium rubrum and the long-day plantChenopodium murale counteracted to a great extent or even canceled the inhibition of flowering due to exogenous indole-3-acetic acid (IAA). This effect was more pronounced with the two substances administered simultaneously than with later application of AVG alone. AVG by itself in some cases promoted the percentage of flowering in bothChenopodium species. Application of IAA to the shoot apex was shown to elevate ethylene production in both species, whereas application of AVG alone was shown to suppress it. Thus, ethylene may be considered an active agent of flowering inhibition brought about by IAA application.

The Developmental Pattern in a Group of Therophytes: I. Seed Dormancy

Summary The occurence and characteristic features of dormancy in ten species of therophytes ( Allysum calycinum L., Arenaria serpyllifolia L., Calamintha acinos (L.) Clairv., Lamium amplexicaule L. Lithospermum arvense L., Medicago minima (L.) Grufbg., Myosotis hispida Schlecht., Thlaspi perfoliatum L., Veronica dillenii Cr., Veronica praecox All.) in xerothermic grasslands has been studied. The laboratory experiments were extended by detailed phenological observations in natural habitats on slopes of the Bohemian Karst and Ceske Středohoři Hills. The experiments revealed the occurence of seed dormancy in all investigated species, with exception of Calamintha acinos. The prevailing type of dormancy seems to be the physiologically unripened embryo. The requirements for after-ripening of about three months duration was established in the following species: Alyssum calycinum, Arenaria serpyllifolia, Lithospermum arvense, Myosotis hispida, Thlaspi perfoliatum Lamium amplexicaule, Veronica praecox. Another two types of dormancy are represented by the impermeability of the seed coats ( Medicago minima ) and most probably by the presence of germination inhibitors ( Veronica dillenii ). The dormancy was broken by puncturing the seed coats in the first case, and by gibberellic acid treatment in the second one. According to our phenological observation and experimental data, dormancy lasts throughout the hot summer season and may be thus considered an important developmental adaptation to fit the local climatic pattern.

Electric Current Inhibits Flowering in the Short-Day Plant Chenopodium rubrum L.

Summary Direct current (DC) of 6 μA was applied to the leaves of the short-day plant, Chenopodium rubrum L., in order to ascertain its influence on flowering. DC of negative polarity, i.e. with the cathode at the leaf tip or at the distal petiole end, applied either within the inductive dark period or during 6 h of light following it, completely inhibited flowering. DC of negative polarity applied to leaves before the dark period or 6 h after its end did not prevent flowering. Thus, the inhibitory DC treatment was only effective during the period when the floral stimulus was apprently transported from the leaves. DC of positive polarity, i.e. with the anode at the leaf tip, applied during the inductive cycle had no effect on flowering. The inhibition of flowering might result from a disruption of the normal transport of the floral stimulus from the leaves.

Auxin in flowering of short-pay and long-dayChenopodium species

The fluctuation of free IAA under 16 h dark period in shoots (receptor organs of photoperiodic induction) and roots of the short-day plant (SDP)Chenopodium rubrum and in shoots of the long-day plant (LDP)Chenopodium murale is very similar. The data reflect the general adjustment of auxin level to day-length rather than changes due to floral induction. However, the shift in phasing of the circadian rhythm of flowering was accompanied by a change in the position of the’ troughs’ of free IAA levels indicating a possible relationship between the two processes. Periods of higher sensitivity to application of IAA (3. 10-4M) inhibitory to flowering have been observed both during the endogenous rhythm of flowering in the SDPC. rubrum and during induction by days of continuous illumination in the LDPC. murale. There exist common traits in the response of LDP and of SDPChenopodium to auxin treatment. Aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, counteracted some flowering inhibitory effects of IAA when applied simultaneously with it. This suggests that auxin effects in modifying flowering might in fact be due to ethylene.

Transgenic tobacco plants with T-DNA phytohormone synthesis genes

Agrobacterium tumefaciens binary vectors carrying kanamycin resistance gene and either C58 T-DNA gene 4 for cytokinin synthesis or genes 1 and 2 for auxin synthesis were constructed and used for transformation of a short-day tobacco Maryland Mammoth. Kanamycin resistant plants were regenerated from a small fraction of transformed tissue and the presence of T-DNA in their genome was verified by Southern blotting. The level of endogenous cytokinin in plants transgenic for gene 4 and the level of endogenous IAA in those transgenic for genes 1 and 2 increased by more than 100 %. A number of morphological characteristics distinguish them from untransformed controls.

Changes in organ growth ofChenopodium rubrum due to suboptimal and multiple photoperiodic cycles with and without flowering effect

The growth changes of cotyledons, leaves, hypocotyls and roots due to photoperiodic induction in short day plantChenopodium rubrum were investigated in relation to flowering. Six-day old plants were induced by photoperiods with a different number of dark hours. We found that the degree of inhibition which occurred during induction in the growth of leaves, cotyledons and roots similarly as the stimulation of hypocotyl is proportional to the length of dark period. The photoperiods with 12, 16 and 20 dark hours bring about marked inhibition of growth and at the same time induce flowering in terminal and axillary meristems. The inhibitory effect of critical period for flowering,i.e. 8 dark hours, is not apparent in all criteria used and even the flower differentiation is retarded. The photoperiods of 4 and 6 dark hours did not affect growth and were ineffective in inducing flowering even if their number has been increased. The experiments with inductive photoperiod interrupted by light break have clearly shown that growth pattern characteristic for induced plants can be evoked in purely vegetative ones. Such statement did not exclude the possible importance of growth inhibition as a modifying factor of flower differentiation. We demonstrated that the early events of flower bud differentiation are accompanied by stimulation of leaf growth. The evaluation of growth and development of axillary buds at different nodes of insertion enabled us to quantify the photoperiodic effect and to detect the effects due to differences in dark period length not exceeding 2 hours.

The shoot apex as the site of an inhibitory effect of applied auxin on photoperiodic induction of flowering in the short-day plant Chenopodium rubrum L.

Summary IAA (3 × 10−4 M) inhibited the photoperiodic induction of flowering applied to the apex of gibberellin-treated Chenopodium rubrum plant during the short day inductive period. This concentration was virtually ineffective when applied to the leaves. No differences in flowering were observed in comparisons with plants where the distance between the cotyledon and apex had not been increased by gibberellic acid treatment. The results obtained with labelled IAA indicate that there is substantial transport of IAA from cotyledon to apex and vice versa in the latter case. Apical meristems thus appear to be the site of the inhibitory action of IAA during the short day induction of Chenopodium rubrum.

Time-dependence of auxin and ethrel effects on flowering in chenopodium rubrum L.

IAA, NAA and ethrel (1 × 10-4M and 3 × 10-4M) was applied to the plumula of Chenopodium plants at different time after the start of photoperiodic treatment and the flowering response was investigated. The inhibitory effect was found with all the applications during the first two days, whereas a stimulatory one on the third and fourth day. We assume this dual effect reflects the differences attained in developmental phase and in the degree of shoot apex differentiation.

The effect of photoperiodic régime on vernalization of winter wheat

Na ozimé pšenici odr. Hodonínská holice byla studována otázka vlivu fotoperiodického režimu na průběh jarovisace.Polní pokusy ukázaly, že krátký den urychluje vývoj, působí-li v dobé jarovisace. Krátký den aplikovaný po jarovisaci ve všech případech vývoj prodlužoval. Při umělém osvětlení nízké intensity a v podmínkách jarovisačních teplot probíhá jarovisace většinou rychleji na dlouhém dni. Jarovisace v temnotě se uskuteĝňuje pouze po přidání glycidů. Předpokládám, že i u zelených rostlin je nahromadění určitého množství ergastického materiálu, zejména glycidů, jednou z podmínek průběhu jarovisace. Tohoto nahromadění může být dosaženo jednou prodloužením osvětlení (v podmínkách optimálních jarovisaěních teplot a při umélém osvétlení poměrně nízké intensity), jindy, v polních podmínkách, krátkým dnem vyvolávajícím specifickou, fotoperiodicky kontrolovanou růstovou reakci inhibující růst.Summary1.Photoperiodic experiments with the effect of short day during vernalization of winter wheat under field conditions have shown that the short day enhances development if applied during vernalization. Short day applied after vernalization prolonged the development.2.At low intensity artificial illumination and under optimal vernalization temperatures vernalization proceeds the faster the longer the illumination. On increasing illumination intensity differences between the effect of short and long day are obliterated. Vernalization in the dark takes place only if saccharides are added.3.It is assumed that even in green plants the accumulation of a certain amount of ergastic material, particularly saccharides, represents one of the conditions of vernalization. This accumulation may be achieved by longer illumination (under conditions of vernalization temperature and low illumination intensity), i.e. by a direct photosynthetic effect, or else by short day (under field conditions) causing a specific, photoperiodically controlled growth reaction which inhibits growth. When vernalization proceeds in the dark saccharides must be supplied.AbstractНа озимой пшениме сортC Годонинская голиц,а изучалсы вопрос влияния фосопериодического режива на течение ырови7ации. В наших исследованиях использован метод полевых фотопериод ических оиытов и ыровизация в разных фотопериодических режимах при искусственвом освещении.Полевые опыты пока зали, что короткий день, ускорыет развитие, если влияет во времы ыровизации. Короткий день, примененный после яровизации во всех случаях тормозил развитие. При искусственном освещении низкой интенсивиости и в условиях яровизационных температур яровиза ция протекает тем быстрее, чем дллинее освещение. Яровизация зеленых растений в темнжте происходит только в случае добавления глицидов. Полагаю, что свет деиствует в течение яровиац,ии прежде всего пос редством фотосинтеза и не только тнпичнки фотопериодической реакцией. Предполат аю, Iчо и у зеленых растений накопление глицидои является одним из услолий течениа яровизации. Этого накопления возможно достичь в одном случае изме нением освещения (в условиях яровизац ионных температур и сравнительно низкой интенсинности освещения), в другом случае, в полевых услопиях, коротким днем, которыщ выгывает специфическую, фотопериодически регулированную ростовую реакцию.

Further Studies on the Inhibitory Action of Direct Electric Current on Flowering in the Short-Day Plant Chenopodium rubrum L.

Summary The inhibitory effect of direct electric current (DC) on flowering (6 µA . plant -1 , cathode at the leaf tips, anode at the roots), applied during the inductive dark period (IDP) or 12 h of subsequent light period to the short-day plant (SDP), Chenopodium rubrum , can be overcome by subjecting the DC-treated plant to another IDP (without further DC treatment). Plants treated with DC within 0-6h or 6-12h of the first IDP flowered due to the second IDP, which followed after 12h of light. Plants treated with DC for the whole first IDP or for 0 - 6 h or 0 -12 h of the subsequent light period flowered only when the second IDP was shifted forward by 24 h, i.e. after 36 h of light. The effect of DC application (6 µA . plant -1 ) to both intact and defoliated plants depended on the position of the electrodes: In all cases when the cathode was placed within the assumed transport path from the leaves being induced to the apex, flowering was inhibited with all tested positions of the anode. The limiting current intensity per plant (i.e. the lowest intensity still causing at least 50 % inhibition of flowering) was 1.5 µA when the cathode was connected to the leaf tips and the anode at the roots, 2.0 µA when the cathode was connected to the leaf petioles and the anode to the roots, 3.0 µA when both electrodes were connected to the leaf blades, and 3.5 µA when both electrodes were connected to the petioles. Interrupted DC treatments showed that the individual treatments are cummulative unless a long enough period between them prevents it. For 1 h treatments breaks of 4 h and for 30 min treatments breaks of 3 h, respectively, are necessary to fully prevent the cummulative effect of the DC effect. The results provide further support for the hypothesis that DC inhibits flowering by interfering with the transport of a > (or other substances necessary for apex evocation) from the induced leaf to the apex.