In broad respect, absolutely; anything that is not optimal range is stress. However, for many plants vernalization is a physiological process required for germination, and thus, I think it is programmed to be a normal condition for a plant, so for Arabidopsis it may not be a stress, but for tobacco (which does not really need vernalization), it may be not.

"Stress" in fact is a lousy concept in plant biology. We can easily deal without using it, because it is not well-defined and usually not measurable. Instead, one can use a concept of optimal/suboptimal/deleterious conditions or whatever other more physiological terms. In this respect, vernalization is an adaptive response to suboptimal conditions.

The answer is yes of course. Heat and cold and many other environmental factors affect the genomic mobile elements and many physiological pathways

Article Environmental Stress Activation of Plant LTR-Retrotransposons

In vernalization, the protein VIN3 represses FLC expression by reducing acetylation of histones in domains of the FLC gene. Subsequent histone methylation by other proteins VRN1 and VRN2 then ensures that FLC expression remains in a stable and repressed state after the plants are returned to warm temperatures. This is the basis of vernalization.

In broad respect, absolutely; anything that is not optimal range is stress. However, for many plants vernalization is a physiological process required for germination, and thus, I think it is programmed to be a normal condition for a plant, so for Arabidopsis it may not be a stress, but for tobacco (which does not really need vernalization), it may be not.

I absolutely agree with you Igor Kovalchuk, if the plant needs a cold period for its development , so it is not considered as stress

i agree with those who think that vernalization is not a stress inducer. but this consideration should be plant dependent. Tropical plants do not need cold period in their life cycle to accomplish their physiological activities. So they will be stressed under this environment. Where as Temperate plants do need vernalization as Igor said and then, will benefit from cold period. Then are not stressed under this environment. So Mathieu, dormancy is different to stress.

No. This cold period is very necessary to development for the plant. Because without this period of vernalization  the plant no complement other phases of dormancy and germination at favorable period.

Cold vernalization is not a stressful process; in many cases it is strictly necessary to allow germination.

For some plants, cold period (vernalization) is necessary to proceed with development, and such plants possess adaptive mechanisms which become switched on during this period, helping a plant to pass through it. Another example are snowdrops and other early spring flowers which normally photosynthesize and flower under high light/freezing temperature - conditions highly damaging to the photosynthetic machinery. I think, it might be helpful to define some “stress markers” like expression of a gene set (maybe, enhancement of expression of autophagy-related genes?) which could indicate that a plant feels “uncomfortable” and is experiencing serious challenges.

cold treatment may or may not be treated as stress because it all depends on the stage of application. like in onion bulb-seed production if given in thermo phase the same temperature say 5-10 0C may not be stress. but at vegetative (bulbing stage) it would be definitely considered as stress.

Vernalization = the vegetative growth phase in spring before the reproductive phase? Then yes, the lower temperature that slows down the vegetative growth can be considered an abiotic stress.

Not really, as you are giving vernalization even before the seed has germinated so you are giving it to a seed in order to make it germinate. The same treatment to a plant after germination will be considered as a stress but not before that. That treatment is a part of its life cycle, like some fish and birds go to warm places for breeding but not otherwise.

I  think there needs to be clear definition what we are talking about here.

To me vernalization is a cold period that causes acceleration of flowering (initiation to anthesis) and subsequent warmer temperatures. The cold period that breaks seed dormancy, to me, should be called stratification.

I also agree that stress is a very vague term when it comes to plants, it is fairly vague for animals, come to think of it!

In Dutch Iris bulbs the optimum temperature for flower initiation is 13 Deg C. I think this is cold enough to allow for a vernalization but warm enough to allow for growth, therefore we get rapid visual appearance of flower primordia. If we put bulbs in a lower temperature the vernilization treatment might be at an optimum temperature, but the expression in terms of anatomical flower appearance is delayed. Therefore we need to be careful to define the developmental stage for which we are defining the optimal conditions. 

No, the abiotic factor which induces injury and hampers normal growth is to be termed as abiotic stress. Plant to plant the interaction plant and a abiotic factor may be different but main consideration is the impact of abiotic factor whether it is causing injury or helping normal growth.

Look at wild plants:

The plant needs vernalization as adaptation to cold period. Flowering after cold season is adaptation to dry and hot summer. Plant accumulates a lot of chemicals that protect tissues from frost damage, and almost stop to grow. Many biannual plants are in fact perennial, and can grow normally for years before flowering without sufficiently cold period. So, cold period is always a stress and plants react to it like to stress.

I agree with most of the colleagues, since a cold period (vernalization) is a prerequisite for flowering in biannuals, it should not be considered stress. Cold weather modifies hormona balance and genome expression in order to allow a plant to fulfill its final destiny: reproduction and death. Nothing negative therefore

Let us look at the definition: “Vernalization (from Latin vernus, "of the spring") is the acquisition of a plant's ability to flower in the spring by exposure to the prolonged cold of winter, or by an artificial equivalent” (Wikipedia). So this is a process and, as such, cannot be a stressing factor. Vernalization is prompted by cold so I think this is the factor under our discussion. In this case, cold can act in two ways: (1) it vernalizes plants and in this case it cannot be considered a stressing factor; (2) after this triggering effect, however, a prolonged cold can hinder plant growth (vegetative, reproductive or both). In this case it acts as a stressing factor, if we define stress as anything that reduces plant growth. Looks like we can speak just about a post-vernalization stress owing to a prolonged cold.