CELLULAR VOLUME AND TISSUE PARTITIONING IN CAPS OF PRIMARY ROOTS OF ZEA MAYS

Cellular and tissue volumes were measured in caps of primary roots of Zea mays. There is an 850% increase in cellular volume as cellular function changes from that of being meristematic (i.e., calyptrogen cells) to graviperception (i.e., columella cells), and a 22% increase in cellular volume during the functional transition from graviperception to the production and secretion of mucilage. Cellular volume does not change significantly after cells cease mucilage production and are sloughed from the cap. Root caps of Z. mays allocate 7.5% of their volume for regeneration, 14.9% for graviperception, 24.3% for the transition of function from graviperception to mucilage production and secretion, and 38.7% for the production and secretion of mucilage. The remaining 14.5% of the cap volume is comprised of cells being sloughed from the cap.     

CORTICAL ONTOGENY IN ROOTS. I. ZEA MAYS

Serial growth stages of young Zea mays primary roots were analyzed for patterns of ground meristem ontogeny. The number of cell layers in the cortex decreases from approximately 15 to 11 during early root growth. The cortex arises mostly by periclinal divisions in the outer portions of the ground meristem at levels 50–150 μm from the meristem tip, although some layers of outer cortex arise beyond 150 μm. The proendodermis contributes 3–5 cell layers to the cortex, but this contribution diminishes during early seedling growth as anticlinal divisions occur in the proendodermis. The relationship between the ground meristem and protoderm changes at the tip of the meristem during root elongation.     

SOLUTE CONCENTRATIONS IN THE PHLOEM AND APEX OF THE ROOT OF ZEA MAYS

Plasmolytic studies utilizing a graded series of mannitol solutions (0.1–1.4 M in 0.1 M increments) were conducted on adventitious roots of Zea mays to determine solute concentrations of cell types at various locations in the root. Results indicated that mature sieve-tube members had the highest solute concentration as determined by their C₅₀ (the estimated mannitol concentration plasmolyzing an average of 50% of a given cell type) of any cell type in the root. In tissue 12 cm from the tip, C₅₀ values calculated for proto- and metaphloem sieve-tube members were 1.15 and 1.19 M, respectively, while in tissue 0.5 cm from the root tip, values for the same cell types were 0.68 and 0.46 M, respectively. The C₅₀ values for sieve elements in tissue 5 cm from the tip were intermediate (1.08 and 1.11 M). Although the companion cells generally plasmolyzed at nearly the same concentrations of mannitol as the sieve elements, their C₅₀ values were slightly lower than adjacent mature sieve elements. The lowest C₅₀ (0.35 M) for any cell type examined was associated with meristematic cells in tissue 0.1 cm from the root tip. Taken collectively, the results indicate that positive concentration gradients exist between mature sieve tubes and meristematic cells of the root apex of maize.     

THE ISOLATION AND CULTURE IN VITRO OF THE QUIESCENT CENTER OF ZEA MAYS

Using 3-day-old seedling roots of Zea mays L., cv. Kelvedon 33, it was possible to remove the root cap by a simple surgical manipulation without damage to the root proper. By a further small cut, the quiescent center (QC) itself was isolated. This double-convex lens-shaped tissue piece 100 X 250 μm is composed of 1000–1500 cells representing only 0.25 mm³ in volume. The explant was demonstrated unequivocally by ³H-thymidine incorporation before excision and then by autoradiography to be composed of the specific cells usually designated the quiescent center. Using sterile techniques, the QC's were placed on nutrient agar slants and allowed to grow in culture. Of a number of nutrient media tested, only a medium supplemented with organic nitrogen components, indoleacetic acid, kinetin and inorganic nutrients plus sucrose (S2M + K -2,4-D) was effective in eliciting development. Thirty to 40 percent of the 150 isolated QC's grown on this medium formed elongated roots, up to 2 cm in length in 3–4 weeks. Roots developing on agar medium showed in their proximal portion a vascular pattern with 5–6 metaxylem elements or variations of this pattern, but as the root elongated, the vascular pattern was progressively reduced in complexity at the more distal end to a small central group of metaxylem elements. When agar-grown roots were transferred after one week in culture to a liquid nutrient medium of the same composition, the initially reduced vascular pattern evident in the proximal tissues became progressively more complex in the distal portion of the root and after 2 cm of elongation, showed an essentially normal primary vascular tissue pattern characteristic of the seedling root.     

THE OCCURRENCE OF WALL PAPILLAE IN ROOT EPIDERMAL CELLS OF AXENICALLY GROWN SEEDLINGS OF ZEA MAYS

Lens-shaped wall papillae, resembling those known to form in response to fungi or mechanical damage, occur in root epidermal cells of axenically grown seedlings of Zea mays. Papillae are most common in the tabular epidermal cells but also occur in younger cells. Not all tabular cells have papillae, and they are more frequent in some seedlings. Where present, there is usually only one papilla per cell and it lies against the outer periclinal wall just proximal to an emerged root hair or near the position where a hair would be expected to form. Electron micrographs show that a papilla is structurally heterogeneous. Papillae fluoresce strongly in the presence of aniline blue even in freeze-substituted material.     

钙调素参与玉米线粒体琥珀酸脱氢酶活性的调节

经DEAE C-32柱纯化的玉米(Zea mays L.)线粒体琥珀酸脱氢酶(SDH),用NAD激酶(NADK)法测定时,无钙调素(CaM)活性,说明不存在游离CaM;而用ELISA法测定总CaM时,却可检测到CaM。纯化的SDH加热处理后,能激活NADK,可能加热释放出游离CaM。纯化SDH的电泳分析表明,天然聚丙烯酰胺凝胶电泳(PAGE)只显示1条主带;而SDS-PAGE则出现67.0kD、30.0kD、16.7kD 3条带,前两条带与SDH的大、小亚基分子量一致,第三条带与CaM电泳迁移率一致。上述结果说明CaM可能与SDH处于结合状态,而且其活性受CaM调节。