Exploring the responses of root morphology and its physiological mechanisms under drought stress is significant for further improving water and nutrient absorption in roots. Here, we simulated drought through hydroponics combined with PEG treatments in tobacco to characterize the changes in tobacco root architecture. Our results showed the total root length, first lateral root number, and first lateral root length were significantly reduced upon increasing drought severity, but the average root diameter and secondary lateral root density increased under certain drought conditions. The change of auxin content in roots under drought stress was correlated with the root diameter and second lateral root density responses. Exogenous addition of the auxin analog (NAA) and the auxin transport inhibitor (NPA), as well as DR5:GUS staining experiments further demonstrated that auxin participated in this physiological process. Meanwhile, brassinolide (BR) exhibited a similar trend. Exogenous addition of BR (EBR) and the BR synthesis inhibitor BRZ experiments demonstrated that BR may participate upstream of auxin under drought stress. PEG treatment significantly up-regulated NtBRI1 at 9–24 h, and promoted the up-regulation of NtBSK2 and NtBSK3 at 48 h and 24 h, respectively, these genes may contribute to the change in root morphology under drought stress. This study shows that auxin and BR are involved in the changes in root morphology in tobacco exposed to drought stress. The elucidation of the molecular mechanism at play thus represents a future target for breeding drought-tolerant tobacco varieties.

为探究烟草株型特征和光合功能适应密植的机制,以中烟100为材料,设置HD(17857株/hm2)、MD(14286株/hm2)、LD(11905株/hm2)3个密度处理,探究种植密度对平顶期烟草第4叶位(L4)、第10叶位(L10)、第16叶位(L16)的光分布、株型特征、光合功能及叶片含氮量的影响.结果表明,密植降低了上部叶的大小和弯曲程度,增加了节长,提高了L4叶位的透光率,大幅降低了L16叶位的透光率;L4叶位的净光合速率和气孔导度均增加,比叶氮也显著增加,而叶绿素含量和比叶重无显著变化.L16叶位的净光合速率和气孔导度在高密度下显著降低,Fv/Fm、Y(Ⅱ)、qP和叶绿素含量也显著降低.密植导致L16叶位行间叶面积指数显著增加,而L4和L10叶位的株间和行间叶面积指数均无明显变化.增加种植密度还使冠层下部分布在行间的叶数增多.由此可见,烟草通过调节冠层叶片姿态改善光环境,适应密植环境,不同位置叶片光合功能对密植适应机制不同,上部叶通过提高光合能力适应高光环境,下部叶通过降低光合速率、加速衰老适应弱光环境,这有利于减少下部叶生物量,促进中上部叶发育,增加中上部叶比例,提高烟叶品质.

为探究油菜素内酯(BRs)对烟草幼苗根系构型的调控机制,选取烤烟品种农大202为试验材料,分析不同浓度外源EBR(2,4-表油菜素内酯)和BRZ(BRs合成抑制剂)处理下烟草幼苗根系构型的差异,通过电镜观察二级侧根根尖横截面变化,并观察烟草转基因DR5::GUS材料根系GUS(β-葡萄糖苷酸酶)染色情况,测定侧根中生长素含量和相关基因表达量,分析根系构型变化与生长素之间的关系.结果表明,EBR可以调节烟草幼苗根长、根系直径与二级侧根密度变化,较低浓度的EBR(0.1 nmol/L)使总根长增加,增幅达到29.0％,但在0.5、1、5、10、100 nmol/L EBR处理下,一级侧根长度与对照(不添加EBR 和 BRZ)相比分别降低 4.6％、9.6％、18.5％、29.6％、36.9％;随着 EBR 浓度的增大(0.1～10 nmol/L),二级侧根密度不断增大,但根系平均直径逐渐减小,BRZ(100～500 nmol/L)处理后烟草根系平均直径显著增大;EBR主要通过调控烟草侧根细胞数目和中柱直径影响烟草幼苗根系直径大小,10 nmol/L EBR处理下烟草二级侧根横切直径较CK显著减少32.5％,中柱直径较CK显著减小25.0％;10 nmol/L EBR处理下,烟草侧根生长素含量较CK显著降低7.1％,500 nmol/LBRZ处理下,侧根生长素含量与CK相比无变化;EBR处理使烟草生长素运输基因家族中PIN3aT、PIN3bS、PIN3bT和PIN11T等基因上调,从而调控根中生长素的分布.可见,油菜素内酯可以调控根中不同部位生长素的水平进而影响烟草根系构型的变化.

为明确施氮量、种植密度及其交互作用对烤烟株型及产质量的调控效应,以'中烟100'品种为试验材料,采用二因素裂区设计,研究施氮量与种植密度对平顶期烟株干物质积累、株型性状、光合效率及烤后烟产量、产值、化学成分的影响.结果表明,随着种植密度的增加,烤烟群体叶面积指数增加,单产显著增加,高密度处理的最大叶叶位下降,单株干物质积累减少.随着施氮量的增加,烟株茎秆增高变粗,叶长、叶宽及叶绿素含量增加,上、中、下部叶干物质积累量提高,烤后烟叶烟碱、总氮含量增加,还原糖、总糖含量降低,化学成分可用性指数(CCUI)先增加后降低.方差分析可知,种植密度对平顶期烟株生物量积累的影响大于施氮量,对烤后烟品质的影响小于施氮量,且施氮量与种植密度的交互作用对产量、产值有显著影响.本研究以施氮量120 kg/hm2、种植密度27750株/hm2处理最佳,上、中、下部叶片CCUI值均大于85分,产量、产值分别达到2388.67 kg/hm2、38442.67元/hm2.表明在密植条件下,适当增加施氮量是弥补单株生产力不足及品质下降的有效措施.综合考虑产量、品质和效益,山东烟区'中烟100'以施氮量120 kg/hm2、种植密度18500株/hm2处理组合为最优,可实现烤烟的优质高效生产.

[目的]建立东南烟稻轮作区烤烟临界氮稀释曲线,探讨氮素营养指数用于诊断和评价烤烟氮营养状况的可能性,为实现烤烟合理施用氮肥提供理论依据.[方法]两年两地共3个田间氮肥用量试验,每个试验共设6个氮水平(N 0、45、90、135、180和300 kg/hm2),分析不同施氮量对移栽后不同天数烤烟地上部和叶片干物质积累量的影响.利用不同时期植株氮浓度和干物质积累量,建立地上部和叶片的临界氮浓度稀释曲线方程和干物质积累方程.结合基于无人机可见光谱平台的烤烟氮浓度无损测定方法,计算氮营养指数,判断烤烟氮营养丰缺情况.[结果]施用氮肥明显增加了烤烟地上部和叶片干物质积累量,不同氮肥处理间差异明显,烤烟地上部和叶片氮浓度随烤烟生长进程而降低;东南烟稻轮作区烤烟地上部及叶片的临界氮素浓度和干物质积累量符合幂指数的关系;模型进行独立验证时,氮限制组的数据均在临界氮素稀释曲线以下,而不受氮限制组的数据均在临界氮素稀释曲线附近.模型拟合的临界氮浓度和植株实际临界氮浓度呈线性相关,地上部和叶片的RMSE值分别为0.55和0.44,标准化均方根误差n-RMSE分别为25％和17％,模型具有较好的稳定性;烤烟氮素营养状况的判定可以通过应用临界氮浓度稀释曲线计算氮营养指数(NNI)实现.随着施氮水平的提高,叶片氮营养指数逐步升高,在氮施用量达到135 kg/hm2,叶片氮营养指数可在1以上,处于氮盈余状态.[结论]东南烟稻轮作区烤烟叶片临界氮素稀释曲线模型(Nc=3.2339×DMleaves–0.475)和叶片氮营养指数能够诊断评价该区域烤烟氮营养状况,从而为优化烤烟的氮素管理提供指导.

遮荫栽培是雪茄外包皮烟叶生产的关键栽培技术.为明确低光强对叶片形态结构的影响及其生理机制,在室内模拟条件下,以雪茄品种H382为材料,设置高中低3个光照强度,分别为T200[200±15μmol/(m2·s)]、T100[100±15μmol/(m2·s)]和T50[50±15μmol/(m2·s)],研究了光强对雪茄叶片的形态特征、叶片组织结构及内源激素含量的影响.结果表明,随光强降低,叶长、叶宽、叶面积及比叶面积显著增加,单叶干质量和比叶重显著降低,植株干物质积累量显著降低.低光照强度(T50)的叶片叶绿素含量低于中、高光照强度处理.中、低光强的叶片上、下表皮厚度低于高光强处理,随光强减弱栅栏组织变薄,海绵组织厚度表现为T200＞T50＞T100,T50处理叶片的海绵组织细胞间隙大,组织疏松.光强减弱,叶片生长素(IAA)和脱落酸(ABA)含量显著降低,但赤霉素(GA3)含量却增加,而玉米素(Zt)含量呈先增加后降低趋势.可见,低光强一方面提高GA3含量,降低ABA含量,促进叶片发育;另一方面降低IAA含量和叶绿素含量,最终叶片变薄,干物质积累量减少.

[目的]分析缺氮条件下烤烟叶片性状变化特征,明确叶片性状与叶绿素含量的关系,为优化烤烟氮肥管理策略提供理论依据.[方法]采用大田试验,以云烟87为材料,设置对照施肥和不施氮肥2个处理,在移栽90 d后比较不同处理叶片性状特征(包括叶片干重、叶面积、比叶重、叶片厚度、叶片密度、叶长、叶宽)和叶绿素含量的差异,分析叶片性状和单位面积叶绿素含量以及单位质量叶绿素含量间的关系.[结果]在缺氮条件下,烤烟中、上部叶的叶片干重、叶面积、比叶重、叶长、叶宽和单位面积叶绿素含量减小,叶片厚度无显著变化.下部叶的叶面积和叶片厚度显著减小.单位叶面积叶绿素含量与比叶重和叶片厚度呈极显著正相关,单位质量叶绿素与叶片厚度呈极显著正相关.[结论]不施氮肥影响了烤烟叶片性状,烤烟通过减小叶面积保持叶片厚度来提高叶绿素含量.

为探明烤烟钾素营养与氮吸收同化能力的关系,明确钾素营养与氮同化互作的可能作用途径,为合理施用钾肥提供理论基础,以烤烟品种K326为试验材料,分析了营养液培养条件下,缺钾后烟草各器官干物质和氮积累量的变化情况,根系形态及根系氮硝酸盐吸收速率和硝酸还原酶活性的变化情况.结果表明,缺钾后烤烟茎和叶片的干物质积累量降低,根系干物质积累量无显著变化;缺钾降低了烤烟总根长、根系体积和根表面积,根平均直径无显著变化;缺钾降低烤烟茎和叶片中的氮积累量,增加氮在根系中的分配,降低在茎中的分配;缺钾处理后根系硝酸盐吸收速率和硝酸还原酶活性显著增加.综上,缺钾后烤烟氮积累量降低的主要原因是由于干物质积累量减少导致植物氮需求减少.

为寻求皖南烟区烟叶生产合理施肥的理论依据,设置了不同氮肥用量和不同钾肥用量的田间小区试验,分析了烤烟农艺性状、干物质积累、养分吸收和肥料利用效率的变化特征.结果表明,随着氮肥用量的增加,烤烟株高、叶片数、上中下部叶的叶长和叶宽明显增加;烤烟冠根比和各器官干物质积累量增加;烤烟根、茎、叶片的氮积累量和钾积累量增加;氮肥用量和烤烟整株氮含量表现为显著正相关,和烤烟整株氮积累量及钾积累量表现为极显著正相关;氮肥利用率没有变化,而氮肥农学效率和氮肥偏生产力显著增加.随着钾肥用量的增加,烤烟农艺性状没有明显变化;烤烟根系中的氮含量,茎和叶片中的钾含量增加,而整株的干物质积累量、氮积累量和钾积累量无明显变化;钾肥用量仅与整株钾含量表现为极显著正相关;各处理间钾肥利用率相对较低,不同钾肥用量间,以钾肥用量最低处理的钾肥利用率、钾肥农学效率和钾肥偏生产力为最高.在本试验中,随着氮肥用量的增加,整株的干物质积累和养分积累量持续增加,氮肥利用率上升,施用氮肥增产效果较明显;随着钾肥用量的增加,整株的干物质积累和养分积累量无显著变化,结合烟叶钾含量和钾肥利用率的结果,皖南烟区适宜钾肥用量存在下降的空间.

Dorsoventral asymmetry of photosynthesis is important for light use patterns, but the asymmetry changes with environments. Photosynthetic asymmetry was have been intensively studied for their role in light use efficiency, but less is know about the impact of light properties on asymmetry. Aimed at the current changing fraction of diffuse light in sky radiation, this study investigated dorsoventral asymmetry of photosynthetic traits in direct, diffuse and self-transmitted light (residual light intercepted by one surface) respectively in an important food and energy crop, Sorghum bicolor L. An unique designed method was used to investigate the specific gas exchange of two surfaces in different light properties. We found that anatomical and morphological traits were obviously different in sorghum leaves, which might cause the photosynthetic asymmetry, the variation of photosynthetic rates and stomatal conductance was significant between two surfaces in direct and self-transmitted light, but insignificant in diffuse light. The abaxial stomatal sensitivity of single stoma was lower, while the higher stomatal density in abaxial surface compensated the weakness in stomatal sensitivity. Comparing to direct and self-transmitted light, diffuse light reduced the stomatal sensitivity, while the degree of decline was higher in adaxial surface, which caused weak dorsoventral asymmetry in photosynthesis. Taken together, the finding of this study suggested that stomatal sensitivity determined the degree of dorsoventral asymmetry in the susceptibility to light properties. The different stomatal sensitivity regulated photosynthetic variation, which was benefit to remain high photosynthetic rate in high and changing light. The findings provided new insight in to dorsoventral asymmetry and impact of diffuse light on photosynthesis in isobilateral leaves.