Cr6+胁迫对小麦幼苗根系生长的影响及DNA损伤效应研究

研究了Cr6+胁迫对3 d和10 d龄小麦幼苗根系生长的影响及DNA损伤效应.结果表明(1)>5 mg/L的Cr6+均显著或极显著降低幼苗根长、根数及根系鲜重、干重,3 d龄幼苗根系生长比10 d龄幼苗对Cr6+胁迫更敏感;(2)所试浓度Cr6+均降低两苗龄幼苗根系DNA含量;5～20 mg/L Cr6+浓度范围内,3 d龄幼苗根系DNA含量下降幅度大于10 d龄幼苗,Cr6+浓度>20 mg/L时,3 d龄幼苗根系DNA含量低于10 d龄幼苗;(3)Cr6+对两苗龄幼苗根系DNA增色效应的影响均呈现随浓度增大先升高后下降的趋势;3 d龄幼苗根系DNA增色效应在5～60 mg/L Cr6+浓度范围内大于对照,Cr6+浓度>60 mg/L时则小于对照;在所试Cr6+浓度范围内,10 d龄幼苗根系DNA增色效应均大于对照.     

根系温度对苋菜生长及光合特性的影响

气候室中研究了根温对苋菜幼苗生长及光合等生理特性的影响。结果表明,苋菜幼苗生长曲线呈S形, 30d苗龄时生长最快, 40d苗龄时每株干、鲜重分别为0.45g和6.79g。20~25℃根温时40d苗龄苋菜生长最快,高根温对生长的危害大于低根温, 40℃根温苋菜根系生长、代谢受害严重。苋菜净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Cs)和胞间CO2分压(Pi)随根温的变化趋势基本一致, 20~25℃根温时,Cs、Pi、Pn和Tr均高,不良根温影响了Cs,使Tr降低, Pi降低,进而影响到Pn。回归分析表明, Pn与Cs、Pn与Pi、Tr与Cs、Pi与Cs均呈显著正相关。说明Cs下降是不良根温影响Pn的主要原因。     

几种旱生灌木种子萌发对干旱胁迫的响应

以不同渗透势的PEG(6 0 0 0 )溶液 (- 0 .3～ - 2 .7MPa)为模拟干旱胁迫条件 ,研究了柠条 (Caraganakorshinskii)、花棒 (Hedysarumscoparium)和白沙蒿 (Artemisiasphaerocephala)种子发芽、幼苗生长和累积吸水率对干旱胁迫的响应 ,讨论了参试种子发芽特性、初生根长度与幼苗建植成活率的关系 .结果表明 ,干旱胁迫下柠条发芽率最高 ,其次为花棒 ,白沙蒿最低 . - 0 .3～ - 0 .6MPa渗透势下白沙蒿发芽 10d的初生根长度显著大于花棒和柠条 (P <0 .0 5 ) ,三者的测量值依次为 7.9、4 .5和 3.1cm .干旱胁迫条件下参试种子发芽率与种子 72h累积吸水率均呈极显著的正相关 (P <0 .0 1) .     

疏花水柏枝幼苗生物量与构件对模拟土壤地下水位变化的响应

通过模拟不同地下水位的方法,对疏花水柏枝（Myricaria laxiflora（Franch.）P.Y.Zhang et Y.J.Zhang）一年生幼苗在不同条件下地上与地下部生物量及构件的变化进行测定,分析幼苗生长对地下水位变化的响应。结果显示：随着地下水位的降低,疏花水柏枝幼苗的生长特征指标均呈先增加后减少的趋势,其中地上、地下部分生物量的最高值分别为0.0438、0.0100 g,最低值分别为0.0177、0.0026 g。幼苗地上部生物量在-10 cm处理水平最高;地下部生物量在-15 cm处理水平最高。幼苗直径、根表面积、株高、主根长度、根体积、一级枝数、二级枝数等指标也分别在-10 cm或-15 cm处理水平达到最高值。疏花水柏枝幼苗主要构件的生长与地下水位的变化存在显著相关性。主成分分析结果表明,幼苗的地下部分更容易受到土壤地下水位变化的影响,幼苗性状症候群随地下水位的变化而发生移动,说明该物种幼苗在不同地下水位时的生长投资策略具有较大差异。     

二氢血根碱对莴苣幼苗根生长及其细胞分裂的影响

以莴苣幼苗为受体,用培养皿法检测从细果角茴香中分离得到的二氢血根碱对莴苣幼苗根生长和根毛发育的影响,并采用根尖细胞有丝分裂检测和单细胞凝胶电泳法对其可能的作用机制进行了初步研究.结果显示:较低浓度(25、50μmol/L)二氢血根碱能显著促进莴苣根的生长,较高浓度(200、300μmol/L)二氢血根碱显著抑制根的生长;二氢血根碱(10、20、30、40、50μmol/L)对莴苣幼苗根毛发育有极显著的抑制作用,且两者均表现了浓度依赖性.较低浓度(25、50μmol/L)二氢血根碱使根尖细胞有丝分裂指数显著增加,而对根尖细胞DNA没有显著影响;较高浓度(200、300μmol/L)二氢血根碱使根尖细胞有丝分裂指数显著下降,同时根尖细胞DNA受到显著性损伤.研究发现,低浓度的二氢血根碱对莴苣幼苗根生长的促进作用主要是由于根尖细胞有丝分裂活力增加所致;而高浓度二氢血根碱对莴苣幼苗根的抑制作用极可能是由于根尖细胞DNA受到损伤,使得细胞分裂活力降低,分裂期细胞数目减少,从而导致根生长受到抑制.     

施肥对红豆树苗木生长、根系结瘤和矿质营养的影响

探讨几种市售肥料对红豆树(Ormosia hosiei)苗木各器官生长发育及养分含量的影响,为培育红豆树优质苗木选用肥料提供参考。以红豆树当年生大田苗为试材,采用3种常见肥料(复合肥、缓释肥和尿素)分3个施肥水平进行施肥试验,测定苗高、地径、根系指标、根系结瘤指标、各器官生物量及N、P、K含量,对不同施肥处理苗木质量进行综合评价。不同施肥处理对红豆树苗木生长、结瘤和矿质营养均有显著或极显著影响。施缓释肥和复合肥的处理表现为随施肥量的增加苗木的生长和生理指标均表现出先增后降趋势,施尿素则表现为随施肥量增加呈逐渐递减趋势。通过隶属函数对苗木质量进行综合评价,表明缓释肥30 g·m^-2为最佳施肥处理,其苗高增量、各根系质量指标、各生物量指标、结瘤数量以及根、茎、叶的N、P、K含量均为最大。红豆树当年生苗木密度为50 株·m-2时,施用缓释肥(N-P-K: 30-6-7) 30 g·m^-2可以有效提高红豆树的苗木质量。     

不同光环境的四川大头茶幼苗的生态适应

将４年生的四川大头茶幼苗置于按全光照百分率为１００％（Ｓ１００）、５５％（Ｓ５５）,３３％（Ｓ３３）和１８％（Ｓ１８）的人控光环境下处理。结果表明,不同光环境的四川大头茶幼勒的叶数,叶面积和叶大小的生长动态具有显著差异,且全光照的幼苗生长动态曲线波动最大,主要是因为日照胁迫所致,Ｓ１００的幼苗地上部分生长最差,Ｓ５５生长最好,后遮阴强度增大而下降;地下根系生长随光强增加而增加,主分量分析能很好地反     

Rice seedlings release momilactone B into the environment

Since the growth inhibitor momilactone B was found recently in root exudates of rice (Oryza sativa L.), 3-day-old rice seedlings were transferred to hydroponic culture and the level of momilactone B released into the environment from the seedlings was measured. At day 15 after transfer, the level of momilactone B in the culture solution was 1.8 nmol per seedling compared with endogenous levels of 0.32 and 0.63 nmol per root and shoot, respectively, suggesting that rice seedlings actively releases momilactone B into the culture solution. This release must occur from the roots because only rice roots were immersed in the culture solution. Momilactone B inhibited the growth of ten cress (Lepidium sativum L.) seedlings at concentrations greater than 3 microM. Ten rice seedlings were incubated with ten cress seeds in a Petri dish containing 1 ml of medium, the medium contained 18 nmol of momilactone B, which came to 18 microM. This level of momilactone B was enough to reveal growth inhibition of the cress seedlings. Release level of momilactone B and its effectiveness as a growth inhibitor suggest that it may play an important role in rice allelopathy.     

Biomechanical Response of the Root System in Tomato Seedlings under Wind Disturbance

Wind disturbance as a green method can effectively prevent the overgrowth of tomato seedlings, and its mechanism may be related to root system mechanics. This study characterized the biophysical mechanical properties of taproot and lateral roots of tomato seedlings at five seedling ages and seedling substrates with three different moisture content. The corresponding root system-substrate finite element (FE) model was then developed and validated. The study showed that seedling age significantly affected the biomechanical properties of the taproot and lateral roots of the seedlings and that moisture content significantly affected the biomechanical properties of the seedling substrate (p < 0.05). The established FE model was sensitive to wind speed, substrate moisture content, strong seedling index, and seedling age and was robust. The multiple linear regression equations obtained could predict the maximum stress and strain of the root system of tomato seedlings in the wind field. The strong seedling index had the greatest impact on the biomechanical response of the seedling root system during wind disturbance, followed by wind speed. In contrast, seedling age had no significant effect on the biomechanical response of the root system during wind disturbance. In the simulation, no mechanical damage was observed on the tissue of the seedling root system, but there were some strain behaviors. Based on the plant stress resistance, wind disturbance may affect the growth and development of the root system in the later growth stage. In this study, finite element and statistical analysis methods were combined to provide an effective approach for in-depth analysis of the biomechanical mechanisms of wind disturbances that inhibit tomato seedlings’ growth from the root system’s perspective.     

Comparison of quantitative trait loci controlling seedling characteristics at two seedling stages using rice recombinant inbred lines

A better understanding of the genetics of seedling characteristics in rice could be helpful in improving rice varieties. Zhenshan 97 and Minghui 63, the parents of Shanyou 63, an elite hybrid developed during the last decade in China, vary greatly with respect to their physiological and morphological traits at the seedling growth stage. In this study, we used a population of 240 recombinant inbred lines derived from a cross between Zhenshan 97 and Minghui 63 to identify quantitative trait loci (QTL) for seedling characteristics. All plant material was grown in hydroponic culture. Data for the following characters were collected at 30 days and 40 days post-sowing: plant height, shoot dry matter weight (SDW), maximum root length, root dry weight (RDW), total dry weight , and root-shoot ratio (the ratio of SDW to RDW). Analysis using composite interval mapping detected 16 QTL for the six traits in 30-day-old seedlings. Of these 16 QTL, Minghui 63 alleles increased trait values at only two of them. The QTL in the vicinity of R3166 on chromosome 5 simultaneously influenced PH, SDW, MRL, RDW, and TDW in the same direction. Twenty QTL were detected for the same traits in the 40-day-old seedlings. However, at this stage Minghui 63 alleles increased trait values at eight QTL. The QTL linked to R3166 also affected PH, SDW, MRL, RDW, and TDW. Only four QTL were common to the two stages. These results clearly indicate that different genes (QTL) control the same traits during different time intervals. Zhenshan 97 alleles had positive effects during the first 30 days of seedling growth, but thereafter the positive effects of Minghui 63 alleles on seedling growth gradually became more pronounced.     

北京东灵山区两种生境条件下辽东栎幼苗补充与建立的比较

 北京东灵山区的人工油松（Pinus tabulaeformis）林中常常混生有萌生的辽东栎（Quercus wutaishanica）种群。局部地带辽东栎与油松形成混交林,在山脊及山坡上部一些特殊生境辽东栎甚至取代油松林成为优势种。为了探讨北京东灵山区辽东栎林的天然更新机制及辽东栎幼苗在人工油松林中的天然更新,在油松人工林的林下和林缘两种生境条件下将辽东栎种子播种于2 cm深的土中,对辽东栎幼苗的补充和建立进行了对照试验。结果显示,在辽东栎结实丰年,两种生境条件下播种后辽东栎种子丢失差异并不显著,而辽东栎幼苗补充和建立方面的差异极显著。由于森林动物特别是啮齿类动物的活动对辽东栎幼苗建立的影响具有二重性：消耗种子与促进萌发,本试验特别关注辽东栎幼苗子叶丢失现象及其丢失后果。由于辽东栎种子萌根较早,在幼苗出土前其粗大的主根长达10～20 cm,并已初步形成根系,表明已有相当比例的营养物质从子叶转移到根部。因此当幼苗出土后如果仅仅只是子叶的丢失对辽东栎幼苗的成活和生长均无明显的影响。通过研究发现辽东栎幼苗期子叶丢失有3种形式：1）仅丢失子叶,幼苗其它部位未受伤害,多发生在林缘生境中,占发芽坚果的29.69%;2）整个幼苗连根被拖出地面,多发生在林下生境,占62.43%;3）在子叶与根颈的连接处主干被咬断,林缘为50.88%,显著高于林下的8.41%。但只有后两种形式才导致幼苗死亡。导致这些现象的原因是由于林缘土壤腐殖质含量低,比较干燥,土质较坚实,以及幼苗出土前坚果主根生长得较长等缘故,当幼苗遭受动物捕食时不会轻易地被拖出地面,拖走的往往仅仅是子叶。至生长季节结束,林缘样方辽东栎幼苗的成活率接近20%,茎干平均高度7.94 cm,芽数11.24·株-1,叶片平均干重为81.14 mg·株-1,且几乎全部由丢失子叶的幼苗所构成;而林下样方辽东栎幼苗的成活率不足2%,茎干平均高度4.74 cm,芽数7.52·株-1,叶片平均干重仅为42.27 mg·株-1,以未丢失子叶的幼苗为主。试验结果表明,林缘及类似林缘的环境条件更有利于辽东栎的实生更新。     

THE EFFECT OF COTYLEDON EXCISION ON THE GROWTH OF PEA SEEDLINGS

Pea plants grown under controlled conditions for 28 days were sampled nine times during this growth period. On each sampling day 80 plants were harvested. Cotyledons were excised from 40 plants and the root-shoot axis allowed to continue growth. The other 40 plants were divided into roots, shoots, and cotyledons; the dry weights of alcohol-water extracts and residues from these organs were determined. Shoot lengths, numbers of nodes, buds, flowers, and fruits of 28-day-old plants, whose cotyledons were excised at different times, were determined. These data indicate that cotyledon excision after the 13th day has no apparent effect on seedling growth, whereas excision before the 13th day reduces growth. Glucose-U-C¹⁴ supplied to attached cotyledons of 6- and 16-day-old seedlings resulted in no major difference in the distribution pattern of recovered label throughout the plant even though 16-day-old cotyledons were depleted of their normal endogenous food reserve.     

不同培育时间侧柏种基盘苗根系生长和分布

以3月直接在培养池中播种培育的侧柏种基盘苗作对照,将同期播种的侧柏种基盘苗进行悬空培养,于6月、8月和10月分别移栽到培育池(分别称为种基盘苗、6月移栽苗、8月移栽苗、10月移栽苗),并于翌年3月挖根,研究不同培育时间对移栽后侧柏幼苗根系生长和分布的影响。结果表明:苗木株高、根分布最大深度、根和地上部干重由大到小依次为:6月移栽苗>8月移栽苗>种基盘苗>10月移栽苗。根冠比由大到小依次为6月移栽苗>8月移栽苗>10月移栽苗>种基盘苗,但除了种基盘苗与6月移栽苗之间差异性显著外,其它处理之间差异性不显著。随着悬空培育时间的延长,空气断根限制了侧柏主根的生长,促进了侧根生长,降低了主侧根长度比。但经悬空培育后,任何处理的移栽苗都没有发生根系盘绕现象,移栽后主根的再生没有受到影响。     

Seedling vigour and the early growth of transplanted rice (Oryza sativa)

Previous studies suggest that the positive response of transplanted rice (Oryza sativa L.) to nursery fertiliser application was due to increased seedling vigour or possibly to increased nutrient content. This paper presents results of two glasshouse experiments designed to test the hypothesis that seedling vigour was responsible for the response of transplanted seedlings to nursery treatments. The aim of the present study was to explore the concept of seedling vigour of transplanted rice and to determine what plant attributes conferred vigour on the seedlings. Seedling vigour treatments were established by subjecting seedlings to short-term submergence (0, 1 and 2 days/week) in one experiment and to leaf clipping or root pruning and water stress in another to determine their effect on plant growth after transplanting. Submerging seedlings increased plant height but depressed shoot and root dry matter and root:shoot ratio of the seedling at 28 days after sowing. After transplanting these seedlings, prior submergence depressed shoot dry matter at 40 days. Nursery nutrient application increased plant height, increased root and shoot dry matter, but generally decreased root:shoot ratio. Pruning up to 60% of the roots at transplanting decreased shoot and root dry matter, P concentration in leaves at panicle initiation (PI) and straw dry matter and grain yield at maturity. By contrast, pruning 30% of leaves depressed shoot and root dry matter by 30% at PI, and root dry matter and straw and grain yield by 20% at maturity. The combined effects of leaf clipping and root pruning on shoot, root and straw dry matter were largely additive. It is concluded that the response of rice yield to nursery treatments is largely due to increased seedling vigour and can be effected by a range of nutritional as well as non-nutritional treatments of seedlings that increase seedling dry matter, nutrient content, and nutrient concentration. Impairment of leaf growth and to a lesser extent root growth in the nursery depressed seedling vigour after transplanting. However, rather than increasing stress tolerance, seedling vigour was more beneficial when post transplant growth was not limited by nutrient or water stresses.     

Root growth dynamics of Aleppo pine (Pinus halepensis Mill.) seedlings in relation to shoot elongation, plant size and tissue nitrogen concentration

Large and high nitrogen (N) concentration seedlings frequently have higher survival and growth in Mediterranean forest plantations than seedlings with the opposite traits, which has been linked to the production of deeper and larger root systems in the former type of seedlings. This study assessed the influence of seedling size and N concentration on root growth dynamics and its relation to shoot elongation in Aleppo pine (Pinus halepensis Mill.) seedlings. We cultivated seedlings that differed in size and tissue N concentration that were subsequently transplanted into transparent methacrylate tubes in the field. The number of roots, root depth, and the root and shoot elongation rate (length increase per unit time) were periodically measured for 10 weeks. At the end of the study, we also measured the twig water potential (ψ) and the mass of plant organs. New root mass at the end of the study increased with seedling size, which was linked to the production of a greater number of new roots of lower specific length rather than to higher elongation rate of individual roots. Neither plant size nor N concentration affected root depth. New root mass per leaf mass unit, shoot elongation rate, and pre-dawn ψ were reduced with reduction in seedling size, while mid-day ψ and the root relative growth rate were not affected by seedling size. N concentration had an additive effect on plant size on root growth but its overall effect was less important than seedling size. Shoot and roots had an antagonistic elongation pattern through time in small seedlings, indicating that the growth of both organs depressed each other and that they competed for the same resources. Antagonism between shoot and root elongation decreased with plant size, disappearing in large and medium seedlings, and it was independent of seedling N concentration. We conclude that root and shoot growth but not rooting depth increased with plant size and tissue N concentration in Aleppo pine seedlings. Since production of new roots is critical for the establishment of planted seedlings, higher absolute root growth in large seedlings may increase their transplanting performance relative to small seedlings. The lack of antagonism between root and shoot growth in large seedlings suggests that these plants can provide resources to sustain simultaneous growth of both organs.     

Adenosylhomocysteinase and adenosine nucleosidase activities in Lupinus luteus cotyledons during seed formation and germination

The activities of adenosylhomocysteinase (EC 3.3.1.1) and adenosine nucleosidase (EC 3.2.2.7) were assayed in extracts from yellow lupin (Lupinus luteus L.) cotyledons at different stages of seed formation and seedling development. Adenosylhomocysteinase activity was demonstrated in all the cotyledon extracts examined. Its lowest level was found in the dry seeds and the highest, in 4-day-old seedling cotyledons. Extracts from the cotyledons of maturating seeds, dry seeds, and seedlings up to the second day of growth exhibited no adenosine nucleosidase activity. Adenosine nucleosidase activity appeared in the cotyledons of 2-day-old seedlings and its highest level was reached in 4-to 5-day-old seedlings. There is no inhibitor of adenosine nucleosidase in the maturating and dry yellow lupin seeds. No activator of a possible zymogen form of adenosine nucleosidase from maturating or dry seeds occurs in the growing seedlings.     

GIBBERELLIN RELATIONSHIPS IN THE ‘ALASKA’ PEA (PISUM SATIVUM)

'Alaska’ peas (Pisum sativum L.) grown under a 16-hr photoperiod at 20 ± 1 C and an 8-hr dark period at 16 ± 1 C in their ontogeny exhibit two periods of sensitivity to applied gibberellin (GA), namely, prior to and subsequent to but not during the linear phase of stem elongation. This paper describes experiments conducted primarily with seedlings. Growth-saturating doses of GA, applied to dry seeds before planting (10⁻³ m) and to the shoot tips of 3-day-old seedlings (10 μg), evoked growth rates equal to the growth rate of etiolated seedlings. Sensitivity of seedlings to applied GA decreased with age through the first 2 to 3 weeks of development; by the time seedlings were about 14 days of age and had four elongating internodes they no longer responded to applied GA. As endogenous growth rate diminished late in ontogeny, the plants again became sensitive to applied GA. Growth response was used as a criterion for determining apparent translocation of applied GA. ‘Alaska’ pea seedlings appeared to transport GA, both acropetally from the cotyledons and basipetally from the shoot tip, to all internodes with remaining extension potential. Excision of both cotyledons at any time during the first 9 days of development caused a significant reduction of growth rate, and applied GA did not restore normal growth rate. No evidence was found that the cotyledons supply endogenous GA to the shoot axis in normal seedling development. It is suggested that the normal growth rate of light-grown ‘Alaska’ peas is correlated with the rate of synthesis of GA and that GA is rate-limiting for stem elongation during early seedling development and during the period of decreasing growth rate and onset of apex senescence.     

The role of ethylene in the regeneration of Helianthus annuus (sunflower) plants from callus

Hypocotyl-derived callus from the Helianthus annuus L. inbred line SS415B regenerated significantly more plants if the seedlings were grown in the light. The difference between light- and dark-grown seedlings was not correlated with differences in seedling ethylene production, but seemed to be due to a difference in sensitivity to ethylene at a specific time during seedling growth. Treating 3-day-old dark-grown seedlings with 10 μ M aminoethoxyvinylglycine (AVG) effectively inhibited ethylene production for at least 7 days. Hypocotyl callus derived from AVG-treated seedlings gave the same amount of regeneration as callus from light-grown seedlings. Promotion of regeneration by AVG was not seen unless the 3-day-old seedlings were grown for 4 additional days prior to culturing hypocotyl explants. The effects of AVG could be reversed by treatment with 1-aminocyclopropane-1-carboxylic acid (ACC) during these 4 days. After the 4 days, ACC was no longer effective.     

南亚热带森林24种乔木的种子萌发和幼苗生长

以膨胀珍珠岩为基质,在光和暗的条件下,对２４种南亚热带森林乔木的种子萌发和幼苗生长进行了研究。种子的形态和重量与种的演替阶段有关,种子的重量也与不同的种有关。不同种的萌发率差异较大,种子较大的种,萌发率较高。肉质果实的种子,开始萌发的时间较长。光和暗条件对萌发率和萌发速度无明显影响。幼苗高度和种子重量呈正相关,这一相关在光条件下比暗条件下更明显。暗条件明显地引起群落演替早期的树种的茎徒长,限制根的生长,而对演替后期种无显著的影响。幼苗地上部分和根系生物量的分配与种的演替阶段有关,也与不同的科有关。幼苗地上部分和根系生物量的分配也受光暗条件的影响,而不受种子重量的影响。根和叶的生物量分配和种在其群落演替阶段有关。幼苗的生物量与种子重量有显著的正相关。幼苗的相对生长率相差较大,在没有营养供应的生长基质中,以演替中间阶段的种的相对生长率较大。幼苗从种子的物质利用效率与种子重量呈负相关,而与种的演替阶段无明显的相关。     

STUDIES ON STRIGA SENEGALENSIS III. IN VITRO CULTURE OF SEEDLINGS. ESTABLISHMENT OF CULTURES

Striga senegalensis seeds were cultured on Knop's and modified Murashige-Skoog's medium. An aqueous root exudate/extract of the host (Sorghum vulgare) was found essential for the germination of seeds in vitro. The seedlings grew better on a medium containing sucrose than on mineral salts alone. Only limited growth was achieved on Knop's medium. Better growth was supported by Murashige-Skoog's medium. By transfer to larger culture vessels seedlings were kept in the latter for several months. The seedlings developed chlorophyllous shoots in light and flowered after 4–4½ months. The successful culture of these seedlings in a simple medium of only mineral salts and sugar indicates that the parasitic seedling depends on the host for only water, mineral salts and sugar and not for more elaborate substances.