Bacterial communities associated with roots impact the health and nutrition of the host plant. The dynamics of these microbial assemblies over the plant life cycle are, however, not well understood. Here, we use dense temporal sampling of 1,510 samples from root spatial compartments to characterize the bacterial and archaeal components of the root-associated microbiota of field grown rice (Oryza sativa) over the course of 3 consecutive growing seasons, as well as 2 sites in diverse geographic regions. The root microbiota was found to be highly dynamic during the vegetative phase of plant growth and then stabilized compositionally for the remainder of the life cycle. Bacterial and archaeal taxa conserved between field sites were defined as predictive features of rice plant age by modeling using a random forest approach. The age-prediction models revealed that drought-stressed plants have developmentally immature microbiota compared to unstressed plants. Further, by using genotypes with varying developmental rates, we show that shifts in the microbiome are correlated with rates of developmental transitions rather than age alone, such that different microbiota compositions reflect juvenile and adult life stages. These results suggest a model for successional dynamics of the root-associated microbiota over the plant life cycle.

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Orientation tuning curves were measured at 10 spatial frequencies ranging from 0.5 to 11.3 cycles per degree (cpd) using a masking paradigm. The stimuli were spatially localized test patterns of 1.0 octave bandwidth superimposed upon cosine grating masks. By using a model that corrects for the nonlinearity inherent in the masking process, we obtain the half-amplitude half-bandwidths (theta 1/2) of Cartesian-separable receptive fields that may underlie orientation selectivity. Additional experiments show that the data are not compatible with separability in polar coordinates (spatial frequency and orientation). The orientation half-bandwidths have been found to decrease somewhat with increasing spatial frequency, going from about 30 degrees at 0.5 cpd to 15 degrees at 11.3 cpd, for both sustained and transient forms of temporal modulation. Similar bandwidths are obtained from data where the test is oriented along 45 degrees. These bandwidth estimates are shown to be consistent with subthreshold summation data as well as physiological data from monkey striate cortex.

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A synthetic, chemically defined medium was developed for the initiation and growth of cell and tissue cultures of red clover (Trifolium pratense L.). The medium is broadly supportive and suitable for the culture of other legume species, including alfalfa (Medicago sativa L.), soybeans (Glycine max L.) and jack bean (Canavalia ensiformis L). Cultural variables for red clover were defined, and it is now possible to routinely establish callus cultures of red clover from reproductive and vegetative explant tissues of both mature and immature plants. Cell suspension cultures with rapid cell division rates have been established from calli by adapting the new medium to liquid culture. Organogenesis was induced in callus cultures, and the recovery of whole plants regenerated from callus has been achieved with the cultivars ‘Altaswede’, ‘Arlington’, ‘Kenstar’, ‘Redman’ and ‘Tensas’, but they did not respond equally well. Regenerated plants have been grown to maturity and were fertile. 3‐Aminopyridine was evaluated and found to possess growth‐modifying properties. It is now possible to investigate the use of tissue and cell culture techniques in red clover breeding programs.

When elements of a parallel network, such as the human brain, are extensively interconnected, the network can exhibit 'cooperative behaviour'. Such behaviour, which is characterized by order-disorder transitions, multi-stable states, and a form of memory called 'hysteresis', has been observed in human stereopsis and has motivated models of stereopsis that incorporate cooperative networks. More recently, cooperative phenomena have also been observed in human visual motion perception. This report strongly supports a cooperative interpretation of motion perception by demonstrating hysteresis in the perception of motion direction. The results agree quantitatively with a mathematical model incorporating nonlinear excitatory and inhibitory interactions among direction-selective elements.

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