Central Vascular Tissue Research Articles

Histological Similarities of Abscission Layers in the Pedicel of Asian and African Rices and Their Relatives.

アジア稲およびアフリカ稲とそれぞれの祖先野生種, および他の9種の野生稲について, 籾離脱部位の解剖形態的特性を調査し, 栽培稲と祖先野生種, および野生種間における比較検討を行った. その結果, アフリカ稲の祖先野生種(O. barthii)には, 栽培稲(O. glaberrima)におけると同じく「完全離層」を有する系統のほかに「部分離層」を有する系統がみい出されたが, アジア稲の祖先野生種 (O. nivara)と他の9種の野生稲には「部分離層」を有する系統はみい出されなかった. 本実験に供したOryza属12種の野生稲では, O.longistaminataを除いて, 離層組織は完熟期にはほぼ完全に崩壊していたが, アフリカ稲の祖先野生種では栽培稲と同じく離層組織と中心維管束の間に厚壁組織が発達していて, 完熟期の離層部位における籾と小枝梗の連絡部(supporting zone)はかなり太かった. ところが, アジア稲の祖先野生種やO. longistaminata など11種の野生稲においては離層部位には厚壁組織がほとんどみられず, 完熟期においては籾は中心維管束だけで小枝梗に連結していたため, アフリカ稲の祖先野生種より非常に脱粒性が強かった. なお, 離層組織の形状には蛮曲型, 直線型およびV字型があり, Aゲノム種ではすべて蛮曲型であった.

Subdomains of the octopine synthase upstream activating element direct cell-specific expression in transgenic tobacco plants.

Previous work has shown that the octopine synthase (ocs) gene encoded by the Agrobacterium tumefaciens Ti-plasmid contains an upstream activating sequence necessary for its expression in plant cells. This sequence is composed of an essential 16-bp palindrome and flanking sequences that modulate the level of expression of the ocs promoter in transgenic tobacco calli. In this study, we have used RNA gel blot analysis of RNA extracted from transgenic tobacco plants to show that the octopine synthase gene is not constitutively expressed in all plant tissues and organs. This tissue-specific pattern of expression is determined, to a large extent, by the 16-bp palindrome. Histochemical analysis, using an ocs-lacZ fusion gene, has indicated that the 16-bp palindrome directs the expression of the ocs promoter in specific cell types in the leaves, stems, and roots of transgenic tobacco plants. This expression is especially strong in the vascular tissue of the leaves, leaf mesophyll cells, leaf and stem guard cells, and the meristematic regions of the shoots and roots. Sequences surrounding the palindrome in the upstream activating sequence restrict the expression of the ocs promoter to fewer cell types, resulting in a reduced level of expression of beta-galactosidase activity in the central vascular tissue of leaves, certain types of leaf trichomes, and the leaf primordia.

A Lipopolysaccharide Mutant ofBradyrhizobium japonicumthat Uncouples Plant from Bacterial Differentiation

The Tn5-containing fragment from a non-nodulating mutant of Bradyrhizobium japonicum, strain ML142, was introduced into B. japonicum strain 61A101c by marker exchange to construct strain JS314. Strain JS314 failed to nodulate several soybean varieties tested. However, on a few varieties nodulelike structures were induced to a frequency of 54% of the plants inoculated. The ultrastructure of these nodules was studied in detail by light and electron microscopy. The nodules were devoid of internal bacteria, possessed central vascular tissue (unlike the lateral vascular tissue of a normal nodule), and exhibited localized cell death of epidermal cells. Study of the cell surface polysaccharides of strain JS314 revealed that the exopolysaccharide of this strain was identical to that of the wild type. However, the lipopolysaccharide (LPS) of strain JS314 showed gross differences from that isolated from the wild-type strain. Specifically, the LPS of strain JS314 appeared to lack the high molecular weight LPS I form, strongly suggesting that the LPS lacks the O-chain. Glycosyl-composition analysis showed that the LPS of mutant JS314 lacked 2,3-di-O-methylrhamnose, 3-O-methylrhamnose, fucose, and quinovosamine. These results indicate that LPS I in B. japonicum is essential for bacterial infection of soybean, but is not required to initiate plant cortical cell division, an early plant response to infection.

Histological peculiarities of the abscission layers of African rice, Oryza glaberrima Steud. and its relation with degree of grain shedding.

アフリカ稲 (Oryza glaberrima Steud.) の浮稲30品種, 普通稲12品種を用い, 収穫適期における脱粒難易強度 (籾と小枝梗の間の抗張強度と抗曲強度) を測定するとともに, 籾離脱部位の解剖形態的特性について調査した。その結果, 浮稲は普通稲より脱粒性が強く, 抗張強度と抗曲強度の相互関係を表す回帰式は, 両稲間で異なることがみられた。しかしながら, 浮稲, 普通稲ともに大部分の品種の籾離脱部位にはアジア稲にみられるのと同じような離層が形成されており, その離層は収穫期までにほぼ完全に崩壊したが, 一部の品種では離層の形成が不完全であった。後者はアジア稲にはみられないタイプの離層で, このような離層を有する品種では抗張強度および抗曲強度が強くsupporting zone (支持帯) の直径や厚壁組織の厚さも大きかった。ところが, 日本の水稲品種の一部にみられるような離層の形成が認められない品種は, アフリカ稲には見出されなかった。なお, アフリカ稲では浮稲, 普通稲ともに抗張強度と抗曲強度は離層が崩壊した部位に残るsupporting zoneの直径や厚壁組織の厚さとの間に, それぞれ0.1%水準で高い正の相関関係がみられた。以上の結果から, アフリカ稲の浮稲が脱粒し易い原因は, 完全な離層を有する品種が多く, supporting zoneの直径や厚壁組織の厚さなどが小さいためであろうと考えられた。

Relation between Grain Shedding and Pedicel Morphology near the Abscission Layer of Japonica-Indica Hybrid Rices Bred in Korea

In order to make clear the reason why there are differences in the grain shedding among varieties of Japonica-Indica hybrid rice, morphology of the abscission region in longitudinal sections of the pedicel was investigated. Also, the strength required to detach rice grain from its pedicel was measured with an unbonded strain gauge transducer and a null balancing recorder. All the examinations were made at harvest time. Experimental materials used were 27 varieties of Japonica-Indica hybrid rice bred in Korea and 7 varieties of their parents. The results obtained are as follows: 1. Degree of grain shedding of Japonica-Indica hybrid rices was similar to that of Indica type parents and weaker than that of Japonica type parents (Table 2). 2. In all the Japonica-Indica hybrid varieties, parenchymatous cells presented in the abscission layer have completely collapsed at the harvest time. Regarding their parents, the parenchymatous cells have collapsed in the Indica type parents such as Peta, IR 8, IR 24, and Taichung native 1, while no abscission layer was observed in the two Japonica type parents, Yukara and Jinheung, and one Indica type parent, Dee-Geo-Woo-Gen. 3. Among the Japonica-Indica hybrid varieties, highly positive correlation was observed between degree of grain shedding and thickness of the supporting zone consisting of the central vascular tissues and the sclerenchymatous cells (Fig. 1, 2 and 3). Since the thickness of the central vascular tissues was almost same among the varieties (mean value: 88±6.6μm), it may be concluded that varieties with the thinner sclerenchymatous tissue situated between the abscission layer and the central vascular bundle are essentially more fragile.

Relationship between Grain Shedding and Abscission Layer in Pedicel of Japonica-Indica Hybrid Rices in Korea

In general, Japonica-Indica hybrid rices in Korea exhibit easy shedding compared with the Japonica type. To obtain detailed information on the grain shedding of Japonica-Indica hybrid rices, thc tensile breaking strength required to detach rice grain from its pedicel was examined by using unbonded gauge type transducer and automatic null balancing recorder. The abscission layer between pedicel and spikelet was investigated anatomically. Varieties Yushin and Milyang 21 of Japonica-Indica hybrid, and Jojeongjo and Akibare of Japonica type rices were used. Yushin and Jojeongjo belong to easily shedding group and other two varieties belong to medium or persistent one. The results obtained are as follows: 1. In both Yushin and Milyang 21 of Japonica-Indica hybrid, tensile breaking strength decreased with time from 1 week after heading, reached the minimum after 3 weeks, and then did not vary until the harvest time. In Japonica type rices, on the other hand, the strength of Jojeongjo decreased slightly with time after heading, while that of Akibare increased gradually with time after heading (Fig. 1). 2. Grain ripening of Japonica-Indica hybrid rice was earlier than that of Japonica type rices. In the former, grain on the upper portion of the ear became to bc almost fully ripe at 3 weeks after heading (Fig. 2). From this result and Fig. 1, it appears that in the Japonica-Indica hybrid rice the decrease in tensile breaking strength is related with its ripening. 3. In the varieties Yushin, Milyang 21 and Jojeongjo, number of grains detached from the abscission region of the pedicel gradually increased with time after heading, while in variety Akibare, number of grains detached from the bent portion of the pedicel increased (Fig. 3 and Table 1). 4. The abscission layers of Yushin and Milyang 21, Japonica-Indica hybrid rice, appear to have one to two layers of large parenchymatous cells, while that of Jojeongjo, Japonica type rice, consists of one layer of somewhat smaller parenchymatous cells with some sclerenchymatous cells. In the former, the splitting in the abscission layer was observed at three weeks after heading, but no such splitting in the abscission layer was observed in Jojeongjo even at harvest time. Furthermore, no abscission layer was observed in the Japanese cultivar, Akibare (Fig. 4). 5. From the above results, it appears that the tensile breaking strength is closely related to the width of supporting zone which is composed of central vascular tissue and sclerenchyma tissue. The occurrence of splitting in the abscission layer probably has no relationship to tensile breaking strength. 6. Based on the abscission layer characteristics, the rice varieties used in this experiment could be classified into three types; i) abscission layer exists and splitting occurs at maturity (Yushin and Milyang 21), ii) abscission layer exists but no splitting occurs until harvest time (Jojeongjo), and iii) abscission layer is absent (Akibare).

Spatial and temporal aspects of cell separation in the foliar abscission zones ofImpatiens sultani Hook

The abscission of leaves fromImpatiens sultani Hook. occurs as the direct result of the weakening of a narrow band of cells running transversely across the base of the petiole. This loss of strength of the abscission zone is due to the breakdown of the central cell wall in two or three layers of cells. The process of wall degeneration is first visible 13 hours after the induction of abscission in a small group of cells found just below the concave groove on the adaxial side of the petiole. As the abscission zone gets progressively weaker the area of cells showing wall breakdown expands, spreading through the parenchyma to the lower side of the stele. The walls of the collenchyma and epidermis along the sides and base of the petiole and the central vascular tissues are the last to break down. Experiments in which the abscission zone was dissected into small pieces were undertaken to investigate whether cell wall hydrolysis was a contagious phenomenon, spreading from cell to cell by direct contact. The results of these investigations indicated that there was little requirement for cell to cell contact in either the temporal or spatial integration of cell wall breakdown.

Conversaziones 1974

CONVERSAZIONES were held this year on 9 May and 27 June. At the first conversazione twenty-seven exhibits and two films were shown. The fine structure of plant roots in relation to transport of nutrient ions and water was demonstrated by Dr D. T. Clarkson of the A.R.C. Letcombe Laboratory, Wantage and Dr A. W. Robards of the Department of Biology, University of York. Two major pathways by which nutrients and water move radially across the cortex towards the central vascular tissue have been distinguished by the use of tracer studies of adsorption by different zones of intact root systems, microautoradiography and electron microscopy. Movement can be apoplastic through cell walls, or symplastic between cells joined by plasmodesmata. As the root ages, structural changes in the endodermis reduce movement in the former pathway but the symplast is not interrupted by the elaboration of endodermal walls because plasmodesmatal connexions remain intact. These observations help explain the contrasting extent to which different ions and water reach the shoot from young and mature parts of root systems.

Sugar uptake by the grape berry: A note on the absorption pathway

(3)H-glucose was fed to excised Sultana grape berries via their pedicels for up to 5 hours. Autoradigraphy showed that the label was distributed throughout the fruit within 1 hour. Microautoradiography of tissue sections taken at a number of points showed that within the pedicel the walls of cortical cells had become heavily labelled, suggesting that the cortical cell walls offered a diffusion pathway for the solutes entering the vascular system from the external aqueous solution. Transport along the pedicel was confined to the central vascular tissue with little radioactivity occurring in the cortical cells. Within the pericarp, the vascular bundles and walls of nearby parenchyma cells had become heavily labelled, indicating that the labelled solute was present within the vicinity of cell walls. The general pattern of (3)H-glucose accumulation by excised berries was similar to the deposition pattern of (24)C-labelled photosynthate within attached fruit.