Jana Pospíšilová

Photosynthesis of plant régénérants. Specificity ofin vitro conditions and plantlet response

Regenerants from tobacco(Nicotiana tabacum L. cv. White Burley) leaf segments cultivatedin vitro in vessels with solid agar medium under usual conditions (plantlets) grew under very low irradiance (I = 40 μxmol m−2 s−1), very high relative humidity (more than 90%) and decreased CO2 concentration (ca) during light period. In comparison with seedlings of a similar number of leaves and similar total leaf area grown in sand and nutrient solution, the plantlets had lower dry mass of shoots and roots per plant and thinner leaves almost without trichomes and epicuticular waxes. Due to a low transpiration rate under high relative humidity the water potential of plantlet leaves was higher than that of seedling leaves and the difference in water potential between leaves and medium was lowei. The rate of water loss from leaves detached from plantlets was considerably faster than that from seedlings under the same conditions (I = 110 μrnol m−2; s−1, temperature 30 °C, relative humidity 50 %). Net photosynthetie rates (Pn) of leaves of plantlets and seedlings measured under saturating I, natural ca and the leaf temperature 20 °C were similar, nevertheless the shape of curves relating Pn to c» indicated some differences in photosynthetie parameters(e.g. saturation of Pn under lower ca> higher CO2 compensation concentration in plantlets than in seedlings). Similarly compensation and saturating I were lower in plantlets than in seedlings. The shape of transpiration curves as well as the expressive linear phases of PN(ca) and PN(I) curves of plantlet leaves indicated ineffective stomatal control of gas exchance. These results were confirmed by microscopic observations of stomatal movementsin situ

Potato transformation by T-DNA Cytokinin synthesis gene

Potato plants were transformed by the A.tumefaciens vector which integrates into the plant genome two foreign genes only: pTi C58 T-DNA gene 4 (ipt) responsible for elevated synthesis of cytokinins and kanamycin resistance gene. Three teratoma clones studied showed approximately 3 times, 6 times and 9 times increased levels of zeatin riboside and zeatin in comparison with untransformed controls and slight increase of the IAA level. Shoots formed roots in agar cultures sporadically, if the increase of zeatin riboside and zeatin levels was not higher than 6 times the control level. The chlorophyll content and net photosynthetic rate decreased with increasing levels of zeatin and zeatin riboside.

Integration of Fhotosynthetic Characteristics during Leaf Development

The formation of leaf structure, the development of the chloroplast as a basic unit of photosynthesis, the synthesis of pigment complexes and the components of the electron transport chain in the thylakoid as the place of the photochemical reactions of photosynthesis have been touched on or thoroughly analysed by many authors. Unfortunately, the major part of the existing literature contains the determination of usually only one or two characteristics which belong to the complex mosaic called “the photosynthetie apparatus”. These findings have already been described in the previous Chapters. The papers with a more synthetic aspect are as rare as those that thoroughly analyse the whole leaf life span or the complete leaf insertion gradient.

Role of water transport in origin of water stress

Intensity of transpiration, intensity of water absorption, water saturation deficit (w.s.d.) in different parts of samples and rate of water transport was investigated in samples from leaf tissue of fodder cabbage and banana-tree.In all experiments (at initial w.s.d. 0% and 20%, in samples from upper, middle and lower leaves of fodder cabbage and from leaves of banana-tree) a distinct gradient of w.s.d. in the direction of transport of water was determined, therefore the limiting factor in the water balance was rate of water transport and not rate of water absorption.The lowest amount of water was always transported within transpiring part of sample. When the initial w.s.d. was 0% not only the water transported by tissue from the environment, but also the water of the leaf tissue itself took part in water lost by transpiration and therefore water stress originated in the whole sample. At an initial w.s.d. of 20%, the rate of water absorption was higher than the rate of water transport and therefore the increase of w.s.d. in the transpiring part of the sample was accompanied by a simultaneous decrease of w.s.d. in the transporting part.An increase in the value of w.s.d. in leaf tissue proportionally increased the resistance of water transport in the liquid phase (on the average from 1·7 . 103 to 6·7 . 103 atm min cm2 g−1) and also in the gaseous phase (on the average from 2·7 . 10−2 to 14·0 . 10−2 min cm−1).It was proved that insufficient rate of water transport can be responsible for the origin of water stress. At the same time the rate of water transport was influenced by the value of the w.s.d. since every change of w.s.d. in leaf tissue not only the gradient of water potential changed but also the resistance to water transport.AbstractU vzorků listového pletiva krmné kapusty a banánovníku byla sledována intensita transpirace, intensita absorpce vody, vodní sytostní deficit (v. s. d.) v různých částech vzorku a rychlost transportu vody.Ve všech pokusech (tj. při počátečním deficitu 0% i 20%, u horních, středních a dolních listů kapusty, u listů banánovníku) byl ve směru transportu vody zjištěn značný gradient v. s.d. limitujícím faktorem ve vodní bilanci tohoto pletiva byla tedy rychlost transportu vody a nikoli rychlost příjmu vody.Nejmenší množství vody bylo vždy transportováno uvnitř transpirující části. Při počátečním deficitu 0% se na vodě vydávané transpirací podílela nejen voda transportovaná pletivem z vnějšího prostředí, ale též vlastní voda listového pletiva a tím vznikal v celém vzorku deficit. Při počátečním deficitu 20% rychlost absorpce vody byla vyšší než rychlost transportu vody a proto zároveň se zvyšováním v. s. d. v transpirující části docházelo k poklesu v. s. d. v části transportní.Se stoupající hodnotou deficitu v listovém pletivu stoupal odpor transportu vody a to jak v kapalné fázi (v průměru 1·7 . 103 až 6·7 . 103 atm min cm2 g−1) tak i v plynné fázi (v průměru 2·7 . 10−2 až 14·0 . 10−2 min cm−1).Bylo prokázáno, že nedostatečná rychlost transportu vody může být příčinou vzniku vodního deficitu. Zároveň rychlost transportu vody byla ovlivňována hodnotou tohoto deficitu, nebot při změně v. s. d. v listovém pletivu měnil se jak gradient vodního potenciálu tak i odpor transportu vody.AbstractИсследовалась интенсивность транспирации, интенсивность абсорпции воды, водный дефицит в различных частях образцов и скорость транспорта воды в образцах ткани листьев кормовой капусты и банана.Во всех опытах (первоначальный дефицит 0 и 20%, ткань верхних, средних и нижних листьев капусты, ткань листьев банана) установлен значительный градиент водного дефицита в направлении транспорта воды. Решающим фактором в водном балансе этих тканей была скорость транспорта воды а не скорость абсорбции.Наименьшее количество воды всегда транспортировалось внутри транспирирующей части образца. При первоначальном дефиците 0% в доле воды расходованной транспирацией участвовала не только вода транспортированная тканью из внешней среды, но и собственная вода листовой ткани и тем возникал дефицит в целом образце. При исходном дефиците 20% скорость абсорбции воды была выше чем скорость транспорта и вследствие этого наряду с увеличением водного дефицита в транспирирующей части понижался дефицит в транспортирующей части.С повышением водного дефицита в листовой ткани повьппалось сопротивление транспорту воды как в жидком состоянии (в среднем от 1,7 . 103 до 6,7 . 103 атм мин см2г−1) так в газообразном состоянии (в среднем от 2,7 . 10−2 до 14,0 . 10−2 мин см−1).Было установлено, что недостаточная скорость транспорта воды может быть причиной возникновения водного дефицита. Одновременно на скорость транспорта воды имел влияние этот дефицит, так как при изменении водного дефицита изменялся как градиент водного иотенциала так и сопротивление транспорту воды.

Water potential, water saturation deficit and their relationship in leaves of different insertion levels

The water potential (Ψw) and the water saturation deficit (δWsat) in leaves of different insertion levels of potted kale plants were simultaneously measured. In non-wilting plantsδWsat gradually decreased andΨw slightly increased from the upper to the lower leaves. During the wilting of the plants induced by decreasing of soil moistureΨw practically decreased paralelly in all the leaves but the same decrease ofΨw was connected with the lowest increase ofδWsat in upper leaves and the highest increase ofδWsat in lower leaves. Not only the values ofΨw andδWsat but also their relationship varied considerably with the leaf insertion levels.

Water potential — water saturation deficit relationship during dehydration and resaturation of leaves

The relationship between the water potential (Ψw) and the water saturation deficit (Δ Wsat) in kale and maize leaf tissue was measured during dehydration and resaturation either of leavesin situ or of cut leaves. The curves relating Ψw toΔWsat were similar in all variants, but at the same values ofΔ Wsat corresponding values of Ψw were always lower in leavesin situ than in cut leaves and during dehydration than during resaturation.

Water balance in leaf tissue

Samples of the leaf tissue (14cm2) were placed in a plexiglass chamber which consisted of three parts. Water absorbed by the leaf tissue on one side of the sample was transported through the middle part of the sample to the opposite side and was transpirated there. The intensity of transpiration the intensity of water absorption and water saturation deficit (w.s.d.) were determined simultaneously in this tissue by gravimetry. Water balance was studied either in saturated samples of leaf tissue or in tissue where w.s.d. (10%, 20%, 30%, 40%) was established in advance. Although conditions for water absorption in leaf segments were optimal, w.s.d. originated in the saturated leaf tissue under all given external conditions (evaporation from 41.7 to 17.8 mg cm−2 h−1). W.s.d. which was established in advance for the most part increased during the experiment and reached even high values (more than 60%). the equilibration was reached only under conditions of low evaporation and initial w.s.d. higher than 20% in young leaves and higher than 30% in adult leaves. A positive correlation between the ratio of the intensity of water absorption to the intensity of transpiration and w.s.d. was found only under conditions of lower evaporation (17.8 and 23.2mg cm−2h−1). The maximal values of w.s.d. were limited in this way.Water balance was studied: 1. in leaf tissue of upper, middle and lower leaves of fodder cabbage, 2. in leaf tissue of middle leaves of young and adult plants of fodder cabbage, 3. in leaf tissue of dicots (fodder cabbage) with different vessel orientation in respect to water transport, 4. in leaf tissue of monocots (banana-tree) with water transport upright to the vessel orientation.Considerable change of water balance was observed when the water transport was prolonged by two incisions in the middle part of the sample.Results of all these experiments revealed the possibility of water stress origin even in leaf tissue sufficiently supplied with water.AbstractVzorky listového pletiva byly umístěny v trojdílných plexitových komůrkách tak, že voda absorbovaná listovým pletivem na jedné straně vzorku byla transportována střední části tohoto vzorku do jeho protilehlé části, kde byla vydávána transpirací. Gravimetrickou metodou byla současně měřena intensita transpirace, intensita absorpce vody a vodní sytostní deficit (v. s. d.) tohoto pletiva. Vodní bilance byla sledována jednak u nasycených vzorků listového pletiva, jednak u vzorků s určitým předem navozeným deficitem (10%, 20%, 30%, 40%). Ačkoliv podmínky pro absorpci vody byly optimální, vznikal při všech zvolených typech vnějších podmínek (výparnost 41,7 až 17,8 mgcm−2 h−1) v nasyceném listovém pletivu deficit. Také předem navozený deficit během pokusu většinou stoupal a dosahoval i vysokých hodnot (přes 60%). K vyrovnané vodní bilanci docházelo pouze při podmínkách nejnižší výparnosti a počátečním deficitu větším než 20% u mladých listů a větším než 30% u starších listů. Také pouze při podmínkách nižší výparnosti (17,8 a 23,2 mgcm−2 h−1) byla zjištěna kladná korelace mezi poměrem intensity absorpce vody a intensity transpirace a v. s. d., takže byly chraničeny hodnoty maximálního deficitu.Vodní bilance byla sledována: 1. u listového pletiva horních, středních a dolních listů kapusty, 2. u listového pletiva středních listů mladších a starších rostlin kapusty, 3. při různé orientaci žilek vzhledem ke směru transportu vody u listů dvouděložné rostliny (kapusta), 4. při transportu kolmo na směr žilek u listů jednoděložné rostliny (banánovník).Značné zhoršení vodní bilance bylo zjištěno při prodloužení transportní dráhy dvěma zářezy ve střední části vzorků listového pletiva.Výsledky všech těchto pokusů ukázaly reálnou možnost vzniku vodního defieitu v listovém pletivu i při jeho dostatečném zásobování vodou.AbstractОбразцы листовой ткани были помешены в плекситовой камере состояшей из трех одинаковых частей таким способом, что вода принятая тканью на одной стороне образца транспортировалась через среднюю часть образца и расходовалась при транснирации противоположной частью ткани. Одновременно была гравиметрически определена интенсивность транспирации, интенсивность абсорбции воды и водный дефицит ткани. Водный баланс исследовался не только у образцов с полным насыщением, но и у образцов с некоторым дефицитом (10, 20, 30 и 40%). Хотя условия абсорбции воды были онтимальными в насыщенной ткани листа возникал водный дефицит при всех избранных типах внешних условий (эвапорация от 11,7 до 17,8 мг см−2 ч−1) Также дефициты 10, 20, 30 и 40% в течение опытов увеличивались и достигали даже более 60%. Равноесный водный баланс происходил только в условиях самой низкой звапорации (17,8 мт см−2 ч−1) и первоначального дефицита около 20% у молодых листьев и около 30% у старших листьев. Также лишь в условиях самой низкой эвапорации (17,8 и 23,2 мт см−2 ч−1) была установлена положительная корреляция между отношением абсорбции и транспирации и водным дефицитом листовой ткани и таким способом найден максимальный дефицит. Исследовался водный баланс 1. ткани верхних, средних и нижних листьев капусты, 2. ткани средних листьев младших и старших растений капусты, 3. при различной ориентировке нерватуры по отношению к направлению транспорта воды у листьев двухдольного растения (капуста) 4. при транспорте воды перпендикулярно к направлению нерватуры у однодольното растения (банан).Значительное ухудшение водного баланса было найдено в случае удлинения пути транспорта воды двумя зарубинами в средней части образцов листовой ткани.Результаты всех этих экспериментов показали реальную возможность возникновения водного дефицита в ткани листьев даже при его достаточном снабжении водой.

Conductances for Carbon Dioxide Transfer in the Leaf

Carbon dioxide passes on the pathway from the atmosphere to the carboxylation sites in chloroplasts through a series of structures differing in physical, chemical and biological properties which more or less control its flow rate.

Variable resistance to water transport in leaf tissue of kale

The constant values of water potential gradient accompanying various levels of water flow rate were found in kale leaf tissue segments. This constancy might indicate the decrease of resistance to water flow as flow rate increased and this decrease of resistance was confirmed.

Carbon dioxide exchange in primary bean leaves as affected by water stress

Net photosynthetic rate decreased sharply to zero in the range of water potential- 8.0 to -10.4 x 105 Pa. The observed decrease in photosynthetic rate was due not only to the decrease in epidermal conductance, but also to the decrease in intraoellular conductance. Both conductances decreased in the same range of water potential. With decreasing water potential photorespiration rate decreased whereas dark respiration rate remained rather unchanged. Simultaneously CO2 compensation concentration increased. These facts constitute an indirect evidence that water stress inhibited not only transport of CO2 from atmosphere to carboxylation sites in chloroplasts, but also its conversion into photosynthates.